Chapter 18 The Northern Belt — continued. Arenig, Llandeilo, and Caradoc formations in the district between the Merrick Hills and the Portpatrick coast-line
The detailed structure of the region lying between the Loch Doon granite mass and the Portpatrick coast-line is of considerable interest from the relation which it bears to the structure of the Ballantrae and Girvan region. Along the southern margin of the belt between Loch Trool and the Water of Luce, anticlines of the Moffat series display a sequence from the Arenig volcanic rocks and overlying cherts to the Glenkiln–Hartfell black shales; while on its northern margin, at Portandea and other localities north of Glen App, a similar succession from the Arenig volcanic rocks and overlying cherts to blue-black mudstones yields a characteristic assemblage of Glenkiln graptolites. Throughout the intervening area abundant evidence may be noticed of the lateral modification of the Glenkiln–Hartfell black shales and of the replacement of the Moffat types of sedimentation by deposits which accumulated nearer shore.
i. Black Shale Bands between Lamachan, near Loch Dee, and Dunragit, near Glenluce
Not far to the north of the line which has been drawn as the base-line of the Llandovery Rocks of the Central Belt between the river Cree and the Water of Luce, a prominent series of axial folds of the Moffat series, though not all quite in the same line of strike, forms a well-marked feature on the map between Curleywee at the south-west corner of the Loch Dee granite mass and Gabsnout in the valley of the Luce (two miles N.W. from Glenluce) — a distance of about twenty miles.
Curleywee and Lamachan. — Beginning at the northeast corner of the belt, the observer finds a great development of cherts and black shales on the Curleywee [NX 45460 76948] and Lamachan Hills [NX 44104 77022], on the south-west margin of the Loch Dee granite mass, where they form precipitous crags, which tower above long lines of debris. A glance at the Geological Map of the district (Sheet 8), shows how the members of the Moffat series are repeated by innumerable folds till the outcrop east of Lamachan Hill is about half a mile in breadth. Unfortunately, owing to the contact metamorphism induced by the granite, these exposures are of little service for zonal classification, as the fossils have in most cases been destroyed. Few graptolites have been obtained in the prolongation of this band south-westwards towards the sources of the Cardorkin Burn [NX 42098 74314], south of the Larg Hill. Two small outcrops of diabase-lava have been noted; one within the contact zone, on the precipitous crag about three-quarters of a mile east of the top of Lamachan Hill, where a narrow band of lava, about fifty feet broad, forming the core of an arch, is succeeded by cherts and black shales on the north side and truncated by a fault on the south side, which brings the black shales in contact with the diabase. The other exposure is met with on the south slope of the Larg Hill, where it forms a small isolated boss, which protrudes through the turf, but of which the relations to the surrounding rocks are concealed. On the crag on the north-west slope of Larg Hill, however, several small arches show the radiolarian cherts in the cores of the folds, succeeded by black shales which pass upwards into flags, shales, and grits. From the black shales in contact with the Arenig cherts, the following characteristic assemblage of Glenkiln graptolites was obtained:
Didymograptus superstes (Lapw.)
Caenograptus gracilis (Hall.)
Lasiograptus bimucronatus (Nich.)
Diplograptus euglyphus (Lapw.)
Diplograptus foliaceus (Murch.)
Diplograptus perexcavatus (Lapw.)
Cryptograptus tricornis (Carr.)
Dicellograptus sextans (Hall.)
Dicellograptus moffatensis (Carr.)
Dicranograptus ramosus (Hall.)
Dicranograptus minimus (Lapw.)
Dicranograptus formosus (Hopk.)
Climacograptus bicornis (Hall.)
From the black shales in the centre of the gairy the forms given in the annexed list were collected:
Climacograptus bicornis (Hall.)
Dicellograptus sextans (Hall.)
Diplograptus foliaceus (Murch.)
Dicranograptus ramosus (Hall.)
Cryptograptus tricornis (Carr.)
Leptograptus flaccidus (Hall.)
Lagbaes. — South-westwards along the strike on the east slope of the valley of the Cree, several folds of the Moffat series make their appearance; one at Cardorkin [NX 38659 71879] and another at Lagbaes [NX 38042 72570] (four miles north-west from Newton Stewart), both being traceable for some distance. Of these, the one east of Lagbaes (Figure 94) and (Figure 95) is the most important, as it reveals Arenig diabase-lava for a distance of 400 yards and upwards of 30 yards in breadth, associated with bright cream-coloured cherts richly charged with radiolaria. Black shales occur in association with the cherts, though not conspicuously developed. About 200 yards to the east of the lava, where the fold is represented in black shales, the following graptolites were collected: Didymograptus superstes, Dicellograptus sextans, Dicranograptus ramosus var. spinosus, Climacograptus, &c. Further east, at a point about half a mile south of Loch Middle [NX 39601 73225], another small outcrop of Arenig lava and chert appears with black shales on the south side of the fold. The volcanic rock is highly decomposed, but the chert is seen adhering to the original surface of the lava. These bands of the Moffat series, with the associated volcanic rocks at Cardorkin and Lagbaes, are traversed by intrusive dykes later than the folding of the strata, which are evidently the apophyses of the Loch Doon and Loch Dee granite mass.
Glenhapple Moor. — [NX 36006 70313] Excellent sections of the Moffat series are visible on Glenhapple Moor, on the ridge between the Cree and the Bladenoch, about five miles north-west of Newton-Stewart (Sheet 4 of the Survey Map). From Garwachie [NX 34190 69316] northwards for a distance of two miles across the moor, a series of compound folds of the black shales trend a few degrees north of east, the whole group being truncated on the north side by a north-east and south-west fault which brings the greywackes of Caradoc age successively in contact with the various subdivisions of the Moffat series. The Arenig volcanic rocks are the lowest beds met with. They rise at two or three places, of which the, most important is about a mile and a quarter to the E.N.E. of Garwachie Farmhouse. Here the volcanic rock can be traced for a distance of 400 yards across the moor; it consists of grey pillowy lava, fine-grained and vesicular, resembling the usual diabase type in the Abington area. On the north side it is brought into conjunction with the Caradoc greywackes by the fault already mentioned. Southwards it is succeeded by the radiolarian cherts and by black shales, of which the horizon has not been proved. Not far to the south-west, the lava reappears on another fold, with the cherts and black shales on both sides, while to the south of this arch of lava minor folds of the black shales reveal small exposures of the cherts. At the southmost limit of the black shales, where they come in contact with the greywackes, the following fossils were obtained: Diplograptus quadrimucronatus, Diplograptus foliaceus, Leptograptus flaccidus, Dicellograptus elegans, Dicranograptus Nicholsoni with the wide angle, Corynoides calycularis. It is probable that the highest zone here represented is that of Diplograptus quadrimucronatus of the Hartfell division. The sediments in contact with these black shales consist of greywackes and grits with bands of shale. The grits weather with a brown crust, and contain galls and bands of blue and black shales yielding graptolites. This arch is traversed by two dykes of diorite, which granulitise the cherts in contact with them.
Along the strike about 300 yards to the north-east, the lava again appears as a knob in a peaty moor, its relations to the surrounding rocks not being visible. Still further to the northeast, black shales crop out, till, at Glenhapple Farm, on the west bank of the Cree, alternations of greywacke and black shales are visible on a glaciated surface.
South-west from Glenhapple Moor to the ruins of Garwachie Farmhouse, nearly continuous exposures of cherts and black shales rise on successive folds. On a prominent knoll, about 200 yards N.N.W. of the loch at Garwachie, a mass of black shales has yielded a few Hartfell forms, viz.: Climacograptus caudatus, Dicellograptus caduceus, Corynoides calycularis, and Diplograptus foliaceus. A short distance to the east of this section, and about the same distance north of the loch, the cherts appear, together with black shales, which contain Caenograptus gracilis and Lasiograptus bimucronatus. It is evident that in the Garwachie area both the Glenkiln and Hartfell groups are represented. Between Garwachie and the river Bladenoch [NX 37703 55136], black shales appear in knolls, where, together with their overlying greywackes, they are altered by intrusive diorite dykes.
Glassoch. — [NX 34697 70599] To the north of the Garwachie band, another parallel outcrop of the Moffat series, about half a mile distant, can be traced at intervals for about two miles. About a mile to the north-east of the river Bladenoch the broadest outcrop is visible. Here the cherts appear, and the black shales and greywackes seem to fold round them. At one point next the greywackes the black shales were found to contain Climacograptus caudatus, Diplograptus foliaceus, Diplograptus quadrimucronatus, Dicellograptus elegans, D. Forchhammeri, Leptograptus flaccidus and Corynoides calycularis. At another place, not far to the north-east, flaggy black shales are crowded with Diplograptus foliaceus. Probably both the D. quadrimucronatus and the Climacograptus caudatus zones are here represented.
Glassoch to Carseriggan. — [NX 34662 70551], [NX 31039 68134] In the bed of the river Bladenoch, and to the south-west of that stream on Carseriggan Moor, several exposures of black shales may be observed with greywackes and shales between. The cherts have not been noticed in the folds. From an outcrop in the Bladenoch River, Diplograptus foliaceus and Corynoides calycularis were obtained, and from another in the field at a bend of the road, about a quarter of a mile west of Ford House, Climacograptus caudatus, Diplograptus foliaceus, Dicellograptus elegans, and Corynoides calycularis were collected. About half a mile to the north of Carseriggan Farmhouse, where there are several outcrops of black shales, they appear at the edge of a peaty hollow, where they have furnished Diplograptus foliaceus, Corynoides calycularis, and Climacograptus. In a quarry at the roadside (south side), 600 yards E.N.E. of the Black Burn, cherts and black shales occur. From a portion of these shales the following species of graptolites were collected: Climacograptus caudatus, Lasiograptus margaritatus, Dicellograptus elegans, Cryptograptus tricornis, and Corynoides calycularis.
Black Burn, Drumabrennan — [NX 29513 67221] Still further to the south-west, at a bend in the Black Burn east of the footbridge, and north of Drumabrennan Farmhouse, black shales rise in the midst of greywackes, the beds dipping to the south-east. On the south bank the greywackes rest on the black shales at the foot of a small escarpment, but a little to the south-west the two groups are brought together by means of a fault. In the bed of the stream, strips of greywacke alternate with black shales, probably as the result of folding. In the centre of the burn, close to the greywackes, a dark, coarse, sandy shale was found to contain Diplograptus quadrimucronatus, D. foliaceus, Cryptograptus tricornis, Retiolites (Neurograptus) fibratus, Dicranograptus ramosus, Dicellograptus sp., Corynoides calycularis, and Acrotreta Nicholsoni. A few yards further down stream, in the bed of the burn on both sides of the ford, flaggy black shales with flinty bands have furnished specimens of Climacograptus caudatus, C. bicornis, Dicranograptus ramosus, and Corynoides calycularis. From the ford down to the second band, a distance of 100 yards or so, the section shows an alternation of greywackes and black shales. For 500 yards to the south-west of the first section described north of Drumabrennan, the black shales are visible at intervals in the burn and by the roadside as far as Drumabrennan School [NX 28656 66406]. Thereafter for upwards of a mile to the south-west the evidence is obscured by peat and drift; the black shales, however, reappear at the roadside west of Balminnoch Lodge [NX 26798 65302]. On the hill slope south-east of Loch Heron and the Black Loch, much-shattered black shales occur in the midst of greywackes, and have supplied only fragments of Dicellograptus and Diplograptus.
Ringdoon, Tarf Water. — On a hill named the Tullmerrick Hill [NX 24366 62508], and chiefly on the north-west slope, mid-way between Ringdoon and Mark Broom Farmhouses, numerous exposures of black shale are to be seen which display the radiolarian cherts at two localities. From a cliff towards the western limit of the hill, close to a small burn, in a large mass of black shale, the following fossils were collected: Diplograptus foliaceus, Climacograptus, Dicranograptus ramosus, and Corynoides calycularis. Towards the northern limit of these exposures, alternations of dark sandy shales and greywackes make their appearance.
Carsecreagh Fell. — [NX 22773 61703] To the S.S.W. of Ringdoon, a great development of the Moffat series measures upwards of a quarter of a mile in breadth. At a spot 650 yards south of Drumpail Bridge, at the head of a dry gully, a small exposure of pillowy lava appears in the middle of charts and mudstones, followed by black shales. The north-west slope of the hill is composed chiefly of cherts and black shales, and the north hill-top of cherts and mudstones. These mudstones, like the cherts, contain radiolaria, which project from the freshly fractured surfaces. These folded members of the Moffat series are evidently truncated by a fault which runs in a north-east and south-west direction at an oblique angle to the axes of the folds of the Moffitt Shales, thus giving rise to a feature that now forms a dryhollow. South of this feature greywackes and shales appear without any representative of the Moffat series.
Ben Leight. — [NX 21352 61221]The structure described in the foregoing paragraph seems to be prolonged to the south-west into Ben Leight, which rises to the south of Loch Strand. The higher part of this hill is composed of black shales, cherts, and mudstones, repeated by numerous folds, the general dip being to the S.S.E.
Camrie. — [NX 19747 60826] In the Canine Burn (Sheets 3 and 4 of the Survey Map), which traverses the south-western prolongations of the bands of black shales on Ben Leight, and falls into the Luce a mile above Glenluce, the relations of the strata are clearly shown. At a point in this stream where it flows north and south, about half a mile N.N.W. of White Cairn Farmhouse, there are frequent repetitions of the cherts and black shales, the cherts appearing on six separate folds within a distance of 120 yards. On the west bank of the stream two fossiliferous localities were found in the black shales. One of these yielded the following forms: Pleurograptus linearis, Leptograptus flaccidus, Diplograptus foliaceus, and Corynoides calycularis. The other locality, about four feet to the south, supplied specimens of Leptograptus flaccidus, Diplograptus foliaceus, D. quadrimucronatus, Dicellograptus caduceus, Dicellograptus Morrisi, D. elegans, and Climacograptus caudatus. This is the only place to the south-west of the river Ken from which Pleurograptus linearis has been recorded. The cherts underlying the Moffat Shales and the succeeding greywackes occur on the east bank of the river.
Though the zonal Glenkiln graptolites were not obtained in this part of the Camrie Burn, there can be little doubt that they occur in these folds. For along the strike of the southmost outcrop of chert, about 200 yards to the south-west, the black shales on the north limb of the anticline, within two inches of the cherts, yielded Dicranograptus minimus. A little further from the cherts, the black shales were found to enclose Hartfell forms, including Climacograptus caudatus, large form of Diplograptus foliaceus, Corynoides calycularis, and Dicellograptus.
About 600 yards north of Honey Pig (Sheet 4 of the Survey Map), the Camrie Quarry [NX 20133 60301] exposes cherts and black shales with Diplograptus foliaceus, Climacograptus caudatus, and Corynoides calycularis. To the north-east, near the parish boundary, a constant reduplication may be traced across the strike of the Moffat series, including the cherts and black shales. These folds merge northwards into the axial fold of Gabsnout, Garviland, and Drumpail. Towards the south-west they can be traced over Camrie Fell towards the Water of Luce, where an extraordinary reduplication of cherts and black shales may be followed for a distance of half a mile across the strike. Some of the rocks here associated with the cherts resemble fine volcanic ashes or tuffs. All the beds, however, are so much cleaved that it is difficult to prove the horizon of the zones by means of graptolites.
A mile to the south-east of Camrie, the radiolarian cherts and black shales appear at Glenhoul, in knolls in the fields and at the roadside [NX 61810 88956]. They are traceable for a distance of about half a mile from Blackhill to a point not far north of Glenhoul. No fossils were obtained from these black shales, but they are believed to represent the Glenkiln–Hartfell group. The strata immediately in contact with them are grits.
Gabsnout, Garviland, and Drumpail. — [NX 18096 60506] In the Water of Luce, at a point two miles above Glenluce and a little below the mouth of Gabsnout Burn, likewise in the latter stream opposite Gabsnout Cottage, black shales have furnished specimens of graptolites characteristic of the Dicranograptus Clingani zone. Again, in the Gabsnout Burn, about 260 yards above the Glenluce road [NX 18310 60537], from black shales in contact with greywackes the following assemblage of graptolites was obtained: Leptograptus flaccidus (Hall.)
Lasiograptus margaritatus (Lapw.)
Dicranograptus ramosus (Hall.)
Diplograptus foliaceus (Murch.)
Cryptograptus tricornis (Carr.)
Climacograptus caudatus (Lapw.)
Climacograptus bicornis (Hall.)
The greywackes are here infolded in the shales, which contain forms characteristic of the Pleurograptus linearis zone. From this spot the black shale bands can be traced at intervals up stream for some distance; at one locality they are associated with black greywackes, probably representing part of the Hartfell shales.
At a point about 500 yards up the Gabsnout Burn [NX 18538 60622], cleaved fissile black shales which occur alongside of a stone fence have furnished no graptolites. A gap in the section intervenes, and about 100 yards further up there is an exposure of the lava on the south bank. In the bed of the burn to the north of this outcrop, mudstones and cherts appear, and for about a third of a mile up stream black shales can be traced at intervals on both banks. Near a bend in the watercourse, S.S.E. of Mid Gleniron Farmhouse [NX 19224 60834], the black shales have yielded Dicranograptus ramosus, Diplograptus foliaceus, and Corynoides calycularis. Immediately to the east of this bend, prominent knobs of coarse-grained dolerite make their appearance. This rock is not seen here in contact with other sediments, but is followed northwards by debris of chert and black shales. A little higher up, however (where Sheets 3 and 4 of the Survey Map join), it occurs in the midst of cherts and black shales in the form of knobs on the moor. A specimen of this rock No. (S7166), taken from a knob about half a mile W.S.W. of Garviland [NX 20819 61414], shows under the microscope "phenocrysts of altered plagioclase in a matrix of lath-shaped plagioclase and ophitic augite, more or less replaced by chlorite and leucoxene".
Eastwards by Garviland to Drumpail Burn alterations of greywacke and black shales appear in knolls, and in the stream section, about 400 yards W.N.W. of Drumpail [NX 22129 62432], three exposures of block shales separated by greywackes may be seen within 100 yards. The southmost band yields Cryptograptus tricornis, Diplograptus foliaceus, and Climacograptus; the middle band gives Diplograptus quadrimucronatus, Diplograptus foliaceus, Leptograptus flaccidus, L. capillaris; and the northmost band contains Diplograptus foliaceus, Dicellograptus moffatensis, Leptograptus flaccidus, and Glossograptus Hincksi. Black shales appear along this line of outcrop for a distance of half a mile.
Glen Plantation (Water of Luce, Sheet 3 of Survey Map). — On the west side of the valley of the Luce Water, two miles above Glenluce, and in the line of strike of the band in Gabsnout Burn, the black shales appear in the stream that flows through the Glen Plantation [NX 17473 60134], where the Lower Hartfell Shales are seen in contact with the overlying greywackes, and can be followed for some distance in a south-west direction. On the Challoch Hill [NX 16339 57925], about a mile east of Dunragit, knolls in the cultivated ground show debris of black shales, for the most part much cleaved. About half a mile north-east of West Challoch Farmhouse [NX 16619 57681], the debris yielded Cryptograptus tricornis and Corynoides calycularis. Again black shales crop out by the side of the road leading to Dunragit, from a point between West Challoch and Ballochjargon Bridge, also in the fields between this road and Challoch Mill [NX 15495 57654]. The radiolarian cherts have not been observed on any of these folds; the black shales are cleaved and shattered, and graptolites are difficult to obtain from them, but fragments of Diplograptus and Corynoides were collected.
ii. Black Shale Bands between Glen Trool and New Luce
Glen Trool (Kirkcudbright, Sheet 8 of Survey Map.). — [NX 41255 80105] In the picturesque valley of the Trool — a tributary of the Minnoch Water — which drains the wild granite tract north-west of Loch Dee, a broad development of the Arenig cherts and Moffat black shales, like the outcrops on Curleywee and Lamachan already referred to, has been largely affected by contact metamorphism produced by the adjacent granite. An interesting feature connected with these outcrops is the marked deflection in the strike as the strata approach the margin of the granite. In the lower portion of the Trool valley the strike is in a north-easterly direction, while to the north of Loch Trool it is deflected to the N.N.E., along a line roughly parallel to the granite boundary. This northerly trend is specially noticeable on the Buchan Hill, about half a mile north of Loch Trool, where the outcrop of the cherts and black shales is about half a mile in breadth. On, this hill also the contact alteration superinduced on these sediments is conspicuous, for in certain black shale bands crystals of chiastolite have been developed alongside of graptolites which have not been wholly effaced; the granulitisation of the cherts, which is such a characteristic feature of the zone near the granite on the Bells range, is manifest here also. Even when we recede from the aureole of metamorphism, graptolites are not readily obtained from many of these outcrops in Glen Trool, owing to the movements to which the beds have been subjected. Evidence has been obtained, however, that the radiolarian cherts in the Trool valley are succeeded by black shales, which yield fossils belonging to the Glenkiln division and the lower sub-zones of the Hartfell black shales. The wonderful plications of the members of the Moffat series are strikingly displayed on the finely glaciated rock slopes above the loch to the east of Glen Troca Lodge [NX 40511 80194]. There the arches of chert appear as oval or lenticular masses of no great size enveloped in corrugated black shales, thus showing how a group of strata, which at this point cannot much exceed a thickness of 100 feet, may, by reduplication, cover a broad area at the surface.
Pulnabrick Burn. — One of the best sections for fossiliferous localities is to be found in the Pulnabrick Burn, which rises on the southern slopes of the Benan Hill, and after traversing many outcrops of the black shale series flows into Loch Trool, about a quarter of a mile west of the shooting lodge. About 500 yards up this stream an exposure of black shales has furnished the graptolites given in the annexed list [NX 40135 79957]:
Didymograptus superstes (Lapw.)
Caenograptus pertenuis (Lapw.)
Caenograptus surcularis (Hall.)
Lasiograptus bimucronatus (Nich.)
Diplograptus foliaceus (Murch.)
Dicellograptus sextans (Hall.)
Dicellograptus Forchhammeri (Gein.)
Leptograptus flaccidus (Hall.)
Cryptograptus tricornis (Carr.)
Corynoides sp.
About 100 yards further up, the following still better assemblage of Glenkiln forms was obtained:
Didymograptus superstes (Lapw.)
Caenograptus gracilis (Hall.)
Caenograptus surcularis (Hall.)
Caenograptus pertenuis (Lapw.)
Cryptograptus tricornis (Carr.)
Climacograptus peltifer (Lapw.)
Clathrograptus cuneiformis (Lapw.)
Lasiograptus bimucronatus (Nich.)
Diplograptus euglyphus (Lapw.)
Diplograptus foliaceus (Murch.)
Diplograptus mucronatus (Hall.)
Dicellograptus sextans (Hall.)
Dicellograptus moffatensis (Carr.)
Dicellograptus Forchhammeri (Gein.)
A few yards higher, an outcrop of black shales yielded Dicranograptus ramosus, Diplograptus foliaceus, Glossograptus Hincksi, and Climacograptus bicornis.
The course of Torr Lane, nearly a mile below Loch Trool, lays bare numerous exposures of black shales, some of which yield graptolites, as, for instance, about three-quarters of a mile to the north-east of Stroan shepherd's house, where at the northern edge of the alluvial fiat they have furnished Dicranograptus ramosus, Climacograptus bicornis, Dicellograptus sp., Diplograptus sp., and Corynoides.
One section to which passing reference may be made displays greywacke in contact with, and apparently interleaved in chert on the hill slope about two-thirds of a mile north-east of Stroan [NX 39340 79464], opposite the road leading to Caldons, and about 250 yards from the Glen Trool road. Here on several well glaciated surfaces, traceable at intervals for 150 yards, the normal radiolarian chert seems to pass upwards into grey greywacke and grit without the intervention of a fault, and at one place on the top of the ridge the two are interbanded. On the north side of the arch the cherts are succeeded by black shales.
In the Minnoch Water near Glencairdiand [NX 36861 79063] and High Minniwick [NX 37461 77482], and also in the river Cree south of Bargrennan Church [NX 35032 76265], the black shales appear on numerous axial folds. At these localities, and also in Glen Trool, the Moffat series passes upwards into sandy shales, greywackes, and grits.
Kirkhoble, Glenruther, Waterside (Sheet 8 of Survey Map). — Between Kirkhoble on the Cree [NX 35542 74668], and Waterside [NX 33509 69215]? on the river Bladenoch, a more or less continuous series of outcrops of the Moffat series reveals the Arenig cherts and Glenkiln–Hartfell black shales. About a mile east of Glenruther Farmhouse [NX 32679 73192] a small exposure of Arenig lava may be seen, and on the moorland, about 300 yards further north, greywackes and grits are apparently interleaved in the cherts, while green mudstones and greywackes are interposed between the cherts and black shales. Along the trend of this band south-west from Glenruther, several imperfect outcrops of shattered black shales appear on le roadside between Knowe School and Waterside.
Tannylaggie, River Bladenoch. — To the west of Bladenoch, for a distance of 500 yards across the strike, a constant repetition of cherts, black shales, and greywackes comes to the surface. In the southmost large outcrop of black shales, evidence was obtained of the occurrence of the Lower Hartfell black shales 600 yards south of Tannylaggie Farmhouse [NX 28755 71489], and 250 yards east of the sheep-ree marked on the six-inch map [NX 28700 71484]. Here, on the moor, among greywackes, a band of platy sandy black shales is charged with the following graptolites: Climacograptus caudatus, C. bicornis, Dicellograptus elegans, D. caduceus, Diplograptus foliaceus, and Dicranograptus ramosus. In the hard flinty bands specimens of Dicellograptus sextans occur.
Towards, the south, overlying this fold of Hartfell black shales, grey shales with dark strains are followed by rusty greywackes (irregularly jointed) with partings of grey and blue micaceous shales.
Northwards, the radiolarian cherts appear on two folds of the Moffat series near the sheep-ree. From the arch nearest the sheep-ree the following Glenkiln fossils were obtained: Didymograptus superstes, Caenograptus gracilis, Dicellograptus sextans, Climacograptus peltifer, C. bicornis, Dicellograptus patulosus, D. Forchhammeri, D. moffatensis, Leptograptus flaccidus, Dicramagraptus ramosus, Diplograptus foliaceus, Lasiograptus bimucronatus, and Corynoides calycularis. This list makes it probable that a portion of the lowest Hartfell black shale may occur here together with the Glenkiln Shales.
From the sheep-ree [NX 28468 71482] northwards for a distance of over 300 yards, the radiolarian cherts and associated sediments crop out in numerous exposures. A remarkable feature of these outcrops is the constant association of greywackes with the cherts in such a way as to suggest that the two types of rock are regularly interbedded. This feature is not confined to the Tannylaggie area; it also occurs in sections further to the south-west and to the north-east in Sheet 8, as already described (p. 396). The ground plan in (Figure 96) shows the relations of the rocks visible in knolls near Shepherd's Cairn, 350 yards south-west of Tannylaggie Farmhouse [NX 28530 71813]. The greywackes occur three times between successive exposures of the cherts as the section is followed southwards from the black shale outcrop. The northmost exposure of chert, which is only about a foot wide, is flanked on the north by black shales yielding Glenkiln graptolites, while greywackes are visible on the south side. This thin layer of chert has the normal characters of the radiolarian zone, being charged with recognisable radiolaria, and possessing a grey tint with conchoidal fracture. The same features characterise the central band of chert, which is about seven feet wide, and presents the nodular character well developed.
The band of black shale to the north of the northmost band of chert consists of alternations of black shales, black flinty ribs, and shaly greywacke bands or flaggy shales. The latter seem to be regularly intercalated in the black shales. A thin film of black shale (about one inch thick), about sixteen inches from the edge of the chert, yielded in abundance characteristic graptolites of the Glenkiln Stales (Comograptus gracilis, Didymograptus superstes, and Dicranograptus minimus). The Hartfell black shales are not visible in this section, the strata being concealed along the line of hollow to the north-west. It is probable that the Glenkiln black shales may here be repeated by folding. North of this hollow greywackes and shales immediately succeed, which are probably of Caradoc age. About 100 yards further north a small fold of black shales appears in the midst of greywackes.
For nearly a mile to the south-west of these exposures at Tannylaggie, the rocks are concealed by drift and peat. On a knoll in the moss, about half a mile E.N.E. of Dirneark [NX 26932 70764], black shales in the midst of greywackes have yielded Diplograptus foliaceus, Climacograptus bicornis, and Leptograptus flaccidus.
Dirneark. — In the knolls at Dirneark Farmhouse [NX 26197 70424] (Sheet 4 of the Survey Map), and in the Black Burn, immediately to the east of the house, the relations of the cherts to the black shales are well displayed. Here also it is observable that grits or greywackes are interposed between the cherts and black shales. In the Black Burn, 200 yards E.N.E. of Dirneark Farmhouse [NX 26430 70457], grits occur on both sides of a core of grey cherts, followed by black shales on both sides of the arch. From the black shales on the south limb the following fossils were obtained Caenograptus gracilis, C. pertenuis, Dicellograptus sextans, Dicellograptus sp., Diplograptus foliaceus, Cryptograptus tricornis, and Climacograptus bicornis. One of the bands on the north limb of the fold was crowded with Caenograptus gracilis.
It thus appears that in this fold the radiolarian cherts are overlain by greywackes, which are in turn overlain by black shales with zonal Glenkiln forms. It is not improbable that some member of the basal Hartfell black shales may occur in the north limb of the arch, though none of the zonal fossils has been obtained. The beds in the arch are isoclinally folded, the dip being to the S.S.E. at high angles. The black shales belonging to the Glenkiln group exposed in this arch in the Black Burn are flaggy and sandy with dark flinty bands.
Confirmatory evidence of the intercalation of greywackes in the cherts is to be found on a knoll, a few yards to the south of the ruins of Dirneark. There the greywackes are intercalated between the bands of cherts, and a thin layer of greywacke separates the northmost band of chert, about a foot thick, from the overlying black shales. In this instance also the black shales which immediately succeed the greywacke yield zonal Glenkiln forms. Westwards (W.S.W. from the ruins at a distance of 400 yards [NX 25561 70266], the Moffat series is to be seen in a peaty hollow, exposed in knolls in the midst of the peat and along the margin of the moss. Here also the volcanic rocks occur. In a knoll in the middle of the peat pillowy grey, compact, and vesicular lava is exposed in an outcrop measuring 20 yards in length, bounded on the south side by red mudstones and cherts. The succeeding strata are buried under peat; another knoll, however, 40 yards to the west, exhibits an arch which shows a core of grey cherts, followed southwards by grits and shales, which are in turn overlain by black shales, yielding Caenograptus pertenuis.
To the north-east of the arch of volcanic rocks, the cherts are visible in a drain in the peat moss, while to the south-east of the same arch, at the margin of the moss, a large exposure of much crushed black shales may be seen. Greywackes occur to the north and south of the hollow. It is evident that these exposures form a series of compound folds. This conclusion is confirmed by the occurrence of the cherts and black shales along several lines to the south-west, to the north of Eldrig Loch, where they pass underneath the peat. For about a mile further to the south-west the evidence is concealed, but the Tarff Water [NX 23847 69272] has laid bare the black shales, alternating with greywackes and shales, which have furnished specimens of Caenograptus gracilis. Beyond this section in a south-westerly direction the evidence is concealed by drift and peat for some distance, as far as the Cross Water of Luce.
Main Water of Luce. — [NX 15237 67436] In the basin of the Water of Luce, important lithological modifications of the Glenkiln–Hartfell Shales are traceable, for both in this stream and in its tributary — the Cross Water of Luce — the black shales containing typical Glenkiln forms are no longer represented by sediments of the Moffat type, and the basal zones of the Hartfell group are represented by grey shales with black strains or seams and blue-black mudstones.
We shall take first the section in the Main Water of Luce which begins north of Kilfeather Loup, about two miles north of New Luce, and extends for a distance of 130 yards down stream. At the north end little streaks of black shale appear in crushed grey shales, and from, one of these bands of blue-black shaly mudstones (two yards broad) the subjoined list of fossils was collected:
Dicranograptus minimus (Lapw.)
Dicranograptus ramosus (Hall.)
Dicellograptus sextans (Hall.)
Chyptograptus tricornis (Carr.)
Climacograptus tridentatus (Lapw.)
Climacograptus Schärenbergi (Lapw.)
Climacograptus bicornis (Hall.)
Glossograptus Hincksi (Hopk.)
Corynoides calycularis (Nich.)
Siphonotreta micula (M'Coy.)
These strata occupy the stream for 21 yards, dipping to the N.N.W. in isoclinal folds. On the further side of them an excellent outcrop of black shales covers a space of from 15 to 20 yards of the section and forms a waterfall. Many of the folds in this exposure are normal, but the radiolarian charts are not visible in the centre of the outcrop. Two thin bands of fireclay are associated with the black shales; the latter are massive and flaggy and quite different in character from the normal Moffat type, with black cherty ribs and partings of sooty shales. The following forms, generally in excellent preservation, and some in great profusion, were obtained from this exposure:
Didymograptus superstes (Lapw.)
Caenograptus gracilis (Hall.) in profusion.
Caenograptus pertenuis (Lapw.)
Lasiograptus bimucronatus (Nich.)
Diplograptus euglyphus (Lapw.)
Diplograptus foliaceus (Murch.)
Dicranograptus minimus (Lapw.)
Dicranograptus formosus (Hopk.)
Dicranograptus ramosus (Hall.)
Dicellograptus sextans (Hall.)
Dicellograptus patulosus (Lapw.)
Dicellograptus Forchhammeri var. flexuosus (Lapw.)
Dicellograptus moffatensis (Carr.)
Climacograptus bicornis (Hall.)
Cryptograptus tricornis (Carr.)
Five yards of the section immediately to the south are occupied by greywackes and shales, but further down the Glenkiln Shales reappear much crushed and broken. After a blank in the section for a distance of nine yards, grey sandy shales with black strains appear, and are repeated by folding for a distance of thirty yards. Within this space the Glenkiln Shales are met with at least four times on separate folds. The southmost exposure of these shales yield graptolites in good preservation, the following forms among others having been recorded:
Didymograptus superstes (Lapw.)
Caenograptus gracilis (Hall.).
Caenograptus surcularis
Dicellograptus sextans (Hall.)
Caenograptus patutosus (Lapw.)
Dicranograptus ramosus (Hall.)
The overlying series of grey shales with black strains occupies the stream section southwards for a distance of a quarter of a mile, the beds being occasionally associated with greywackes and grits. The black seams yield fragments of graptolites.
Cross Water of Luce. — [NX 18202 67968] In this stream, which lies to the east of the Main Water, evidence is obtained of the occurrence of Glenkiln Shales of the type just described, associated with grey shales and black seams yielding fossils of a higher zone. About two miles to the north of New Luce, north of a prominent bend in the Cross Water of Luce, west of Dougaries Farmhouse, greywackes and grits appear in the stream, while at the bend itself dark blue micaceous shales are met with which yield large specimens of Diplograptus foliaceus, Climacograptus bicornis, Cryptograptus tricornis, and Dicellograptus. A few yards down stream the following graptolites were got in a thin band of black shales:
Dicellograptus sextans (Hall.)
Dicellograptus sp.
Diplograptus foliaceus (Murch.)
Climacograptus bicornis (Hall)
Cryptograptus tricornis (Carr.)
Dicranograptus ramosus (Hall.)
A few yards lower, massive flaggy black shales have supplied the following characteristic Glenkiln assemblage:
Caenograptus pertenuis (Lapw.)
Diplograptus euglyphus (Lapw.)
Dicellograptus sextans (Hall.)
Dicellograptus Forchhammeri var. flexuosus (Lapw.)
Dicellograptus moffatensis (Carr.)
Climacograptus bicornis (Hall.)
Cryptograptus tricornis (Carr.)
A blank in the section occurs at this point, but at the old bridge greywackes appear.
From the evidence of this section we may conclude that the grey shales with black strains that enclose graptolites common to both the Glenkiln and Hartfell divisions probably represent the basal portion of the Hartfell group in this region, or at least the passage beds between these two divisions, and further, that to the south of the Kilfeather bands of Glenkiln Shales in the Luce Water, the coarser sediments lying in isoclinal folds between Kilfeather and Gabsnout are mainly if not wholly of Caradoc age.
Portpatrick district
Black Shale Bands of Morroch Bay, Colin, and Garthland
Morroch Bay. — [NX 01672 52373] The clear and well-nigh continuous coast section south of Corsewall Point, in Wigtownshire (Sheet 3 of Survey Map), presents at one locality an admirable development of the Arenig cherts and Glenkiln–Hartfell black shales. These strata are specially displayed in Morroch Bay about a mile and a half south of Portpatrick. In point of clear exposures of the various zones and fine preservation of the zonal forms of graptolites, this is one of the most important sections of the Moffat series in the south-west of Scotland.
The beach of Morroch Bay between the limits of high and low tide, though in places covered with shingle, shows a more or less continuous section of the Moffat series for a distance of a quarter of a mile across the strike. Its breadth at low tide measures from 100 to 150 yards. It thus furnishes special opportunities for following the sub-zones along the strike. A narrow strip of raised beach, from 30 to 90 yards broad, skirts the present beach. Inland the old cliff line rises to a height of 100 or 150 feet, and likewise furnishes a more or less continuous section of the strata.
At the southern headland of the bay [NX 01751 52255], a prominent cliff consists of grey sandy micaceous shales, mudstones like the type of the Barren Mudstones of Moffat, and greywackes with calcareous nodules, the greywackes measuring from one to three feet thick. These strata dip to the S.S.E. at high angles. A fault skirts the base of this cliff, and a thin black shale occurs near it, the horizon of which has not been proved. A few yards from the cliff, and close to a stone fence that skirts the southern termination of the raised beach, a small exposure (about three feet across) of Glenkiln Shales with radiolarian cherts displays black flinty ribs with thin sooty partings or layers of black shales (2I, (Figure 98)), from which the following fossils have been collected:
Caenograptus gracilis (Hall.)
Caenograptus pertenuis (Lapw.)
Cryptograptus tricornis (Carr.)
Climacograptus peltifer (Lapw.)
Diplograptus euglyphus (Lapw.)
Diplograptus foliaceus (Murch)
Dicellograptus moffatensis (Carr.)
Dicellograptus sextans (Hall)
Dicellograptus intortus (Lapw.)
Greywackes occur a few feet to the north (3, (Figure 98)), followed by greenish mudstones stained red in places, below high tide mark. Next comes a ridge of black shales (2I, (Figure 98)), highly contorted and bounded on both sides by faults which bring them in contact with green ashy mudstones. This exposure presents the characters of the Moffat type of the Glenkiln Shales, with black flinty ribs from one to four and six inches thick, alternating with genuine black shales. It has yielded the following list of characteristic Glenkiln fossils:
Didymograptus superstes (Lapw.)
Caenograptus gracilis (Hall.)
Caenograptus nitidulus (Lapw.)
Caenograptus pertenuis (Lapw.)
Caenograptus surcularis (Hall.)
Lasiograptus bimucroratus (Nick)
Diplograptus euglyphus (Lapw.)
Diplograptus foliaceus (Murch.)
Diplograptus (Hallograptus) mucronatus (Hall.)
Climacograptus bicornis (Hall.)
Climacograptuspeltifer (Lapw.)
Cryptograptus tricornis (Carr.)
Dicranograptus zic-zac (Lapw.)
Dicranograptus formosus (Hopk.)
Dicranograptus ramosus(Hall.)
Dicranograptus rectus (Hopk.)
Dicellograptus Forchhammeri (Gein.)
Dicellograptus patulosus (Lapw.)
Dicellograptus sextans (Halt)
Dicellograptus intortus (Lapw.)
Dicellograptus elegans (?) (Carr.)
Leptograptus flaccidus (Hall.)
Glossograptus Hincksi (Hopk.)
Sponge.
North of these black shales a succession of green mudstones occupies the beach for a distance of six yards, when another exposure of black shales is met with, yielding Hartfell forms (3II, (Figure 98)). This exposure, which is about 40 yards down the beach from the cottage at the south side of Morroch Bay, gradually thins out seawards, is about six feet broad, and contains outliers of grit. This lenticular patch is apparently truncated by faults on both sides, which bring the black shales in contact with green mudstones. These shales have furnished Diplograptus quadrimucronatus, Leptograptus flaccidus, and Diplograptus foliaceus in abundance, Dicellograpti in abundance on one slab, Corynoides calycularis, Climacograptus bicornis, peculiar variety, and Dicellograptus Forchhammeri. This assemblage proves that the shales belong to the Lower Hartfell group, and probably to a high sub-zone of that subdivision of the Moffat series.
Northwards the green mudstones (C, in (Figure 98)) may be followed as far as the cottage at the south end of the bay, where they are succeeded by red mudstones. The latter are pierced by an intrusive mass of igneous rock, which sends branching veins into them (Fig 98). Further north they are followed by grey radiolarian cherts and mudstones, well seen on the beach and dipping E.S.E. at high angles. The hard ribs of radiolarian chert project above the general surface of the interleaved mudstones. These are succeeded in turn by the Glenkiln black shales, and at the junction the cherts alternate with thin black shales, the latter yielding a minute Climacograptus. The space occupied by the green and red mudstones and the radiolarian cherts and mudstones from the exposure of Hartfell black shales to the Glenkiln black shales is about 54 yards.
The Glenkiln black shales (2I, (Figure 98)) to the north of the mass of cherts and mudstones have the normal characters of the Moffat type, inasmuch as they consist of alternations of black cherty ribs and black shales, followed by black shales. They have yielded the following assemblage of fossils:
Didymograptus superstes (Lapw.)
Dicranograptus zic-zac (Lapw.)
Thamnograptus scoticus (Lapw.)
Caenograptus nitidulus (Lapw.)
Diplograptus euglyphus (Lapw.)
Diplograptus oliaceus (Murch.)
Diplograptus perexcavatus (Lapw.)
Cryptograptus tricornis (Carr.)
Lasiograptus.
Dicellograptus sextans (Hall.)
Dicellograptus patutosus (Lapw.)
This important development of the Glenkiln Shales, occupying the coast section for 21 yards, is traversed by faults and dykes. It is followed northwards by the green ashy mudstones and cherts, about 14½ yards broad, to the edge of a massive dyke (No. 2), about 12 yards in breadth, which pierces the black shales and mudstones ((Figure 98)). The black shales (2I, (Figure 98)) again appear along part of the south side of this dyke. They are separated from the green ashy mudstones by a fault trending south. From the black shales close to dyke No. 2 the following species of fossils have been collected:
Didymograptus superstes (Lapw.)
Caenograptus gracilis (Hall.)
Caenograptus nitidulus (Lapw.)
Diplograptus euglyphus (Lapw.)
Diplograptus foliaceus (Murch.)
Diplograptus perexcavatus (Lapw.)
Cryptograptus tricornis (Carr.)
Dicranograptus zic-zac (Lapw.)
Acrothele granulata (Linnr.)
Northwards these black shales extend for a distance of 40 yards, until they are followed by another small exposure of the cherts, bounded on both sides by faults. A few yards to the south of these cherts, a layer in the black shales contains Corynoides calycularis in profusion, which may belong to the Lower Hartfell group. About four yards to the north of this small development of the cherts, an exposure of Hartfell black shales displays such an abundance of specimens of Glossograptus Hincksi that it has been named the Glossograptus Hincksi Band.
Glossograptus Hincksi (Hopk.) abundant.
Dicranograptus ramosus (Hall.)
Dicranograptus Nicholsoni (Hopk.)
Dicranograptus Nicholsoni wide-angled var.
Cryptograptus tricornis (Carr.)
Diplograptus foliaceus (Murch.)
Climacograptus tubuliferus (Lapw.)
Climacograptus tricornis (Hall.)
Climacograptus tridentatus (Lapw.)
Acrothele granulata (Linnr.)
Another band in this mass of Hartfell black shales yielded:
Glossograptus Hincksi (Hopk.)
Lasiograptus Harknessi (?) (Nich.)
Cryptograptus tricornis (Carr.)
Diplograptus foliaceus (Murch.)
Climacograptus bicornis (Hall.)
Dicranograptus ramosus (Hall.)
Dicellograptus Forchhammeri (Gein.)
Dicellograptus flexuosus (Lapw.)
Dicellograptus moffatensis (Carr.)
Dicellograptus small variety, in large numbers.
Northwards the black shales are traversed by a third massive dyke, about nine yards across, the distance between dykes No. 2 and No. 3 being about 64 yards (Figure 97) and (Figure 98). To the north of No. 3 the shore is occupied by black shales for a distance of 43 yards, the radiolarian cherts coming to the surface on several small folds. At this point in the coast section the Moffat Shales are truncated by a fault trending to the north. Folded Glenkiln Shales succeed on the north side of this fault, while further north, nearly opposite the point where an ivy-covered wall crosses the raised beach from the old sea cliff, greywackes are infolded in the Hartfell black shales. Here the greywackes lie in narrow synclinal folds, as shown in (Figure 97). From the black shales in contact with the greywackes at this locality (3, 3II, (Figure 98)) the following fossils were obtained: Diplograptus quadrimucronatus, D. foliaceus, Dicellograptus, Leptograptus flaccidus (in abundance), Retiolites (Neurograptus) fibratus, and Corynoides calycularis. This layer appears to be on the horizon of the Diplograptus quadrimucronatus zone, at the extreme north end of the bay.
Northwards, beyond a fourth prominent intrusive dyke that pierces the Moffat series on the beach (Figure 98), a series of sharp isoclinal folds repeats the members of the Moffat series and the overlying greywackes. In the midst of these folds small exposures of the cherts show that an ascending series may be traced here from the radiolarian cherts through the Glenkiln–Hartfell Shales to the greywackes.
This belt is abruptly truncated northwards by a fault which brings the greywackes and black shales to the south in contact with the radiolarian cherts to the north. Here, again, a broad development of the radiolarian cherts — upwards of 52 feet across — spreads over the beach, followed by an exposure of Glenkiln black shales, from which the following fossils have been collected:
Thamnograptus scoticus (Lapw.)
Cryptograptus tricornis (Carr)
Lasiograptus bimucronatus (Nich.)
Diplograptus foliaceus (Murch.)
Glossograptus Hincksi (Hopk.)
Climacograptus bicornis (Hall.)
Dicellograptus sextans (Hall.)
Leptograptus flaccidus (Hall.)
These beds are abruptly truncated by a fault trending to the south. The outcrop of radiolarian cherts and black shales lies to the west of the northmost cottage in the bay.
We have now reached an important part of the section in Morroch Bay, where the Hartfell black shales and the overlying grits (3II, 3, (Figure 98)) are repeated by numerous sharp isoclinal folds that dip southwards. Excellent opportunities are afforded of proving the horizon of the black shale sub-zone in contact with the greywackes. The assemblage of graptolites seems to show that it represents the Diplograptus quadrimucronatus zone of the Hartfell black shales. The greywackes and shales which rest to all appearance conformably on the Hartfell black shales must thus represent the Barren Mudstones of the Moffat series, and possibly the very highest sub-zone of the Hartfell black shales. If this inference be correct, then it is apparent that the type of sedimentation is here widely different from that which prevails along the strike of the Moffat region.
Another important feature of the section in the northern part of the bay is the reduplication of the strata by isoclinal folding and the "nosing out" of the synclines of greywacke that overlie the Hartfell black shales. This part of the section thus displays a representation in miniature of the general type of structure which prevails throughout the Silurian Tableland.
At the base of the sea cliff, at the north end of Morroch Bay, where a wall bounds the northern limit of the raised beach near high tide mark, a sharp syncline of grit lies in the Hartfell black shales (3II, (Figure 98)). From the band immediately in contact with greywackes the following fossils were obtained:
Diplograptus quadrimucronatus (Hall.)
Climacograptus bicornis (Hall.)
Dicranograptus ramosus (Hall.)
Cryptograptus tricornis (Carr.)
Cryptograptus Nicholsoni (Hopk.),
Leptograptus flaccidus (Hall.) wide-angled var.
Dicellograptus sp.
The following additional forms were obtained from the black shales a little further from the greywackes:
Dicellograptus moffatensis (Carr.)
Leptograptus capillaris (Carr.)
Leptograptus Forchhammeri (Gein.)
Climacograptus caudatus (Lapw.)
Diplograptus foliaceus (Murch.)
Corynoides calycularis (Nich.)
A striking feature of these shales is the assemblage of forms on the same slab, viz.: Diplograptus quadrimucronatus, Dicranograptus ramosus, and Climacograptus bicornis.
The narrow outlier of greywacke is followed on the south side by several feet of Hartfell shales, which, along the strike seawards, have supplied the fossils given in the accompanying list:
Leptograptus flaccidus (Hall.)
Leptograptus flaccidus pathological var.
Dicellograptus moffatensis (Carr.)
Diplograptus foliaceus (Murch.)
Diplograptus quadrimucronatus (Hall.)
Diplograptus sp., abundant.
Retiolites fibratus (Lapw.)
Climacograptus bicornis (Hall.)
Corynoides sp.
Below the high tide mark, and rather to the north of the strike of the bands just described, seven lenticular patches of black shales appear among the greywackes, apparently forming isoclinal arches in the overlying sediments. From one or more of these bands the following forms were obtained: Leptograptus flaccidus, Diplograptus quadrimucronatus, D. foliaceus, Cryptograptus tricornis and Dicellograptus.
The sediments which occupy the coast for the next 300 yards in a westward direction consist of greywackes, pebbly grits with partings of shale, and grey mudstones.. Near this point on the cliff, at Bellone Cove, two thin bands of black shale which occur among the greywackes have yielded Diplograptus quadrimucronatus, D. foliaceus, Leptograptus flaccidus, Leptograptus capillaris, Dicellegraptus Forchhammeri, and Climacograptus tubuliferus.
Colfin Station. — North-eastwards from Morroch Bay, few exposures of black shale are to be found, which may be accounted for by supposing that these strata gradually pass under higher sediments when traced in that direction. The first satisfactory outcrop is seen in a quarry about two miles E.N.E. of Morroch Bay, and 500 yards S.S.E. of Cowend [NX 04032 54084]. Here greywackes dipping S.S.E. are accompanied by two feet of black shales, which contain Diplograptus quadrimucronatus in excellent preservation, Leptograptus flaccidus, Diplograptus foliaceus, Corynoides calycularis, and Climacograptus bicornis. On the south-west slopes of the Bine Hill [NX 05146 54403], from fragments of black shale visible in the fields, Diplograptus foliaceus and Climacograptus have been collected.
Glenlaggie. — [NX 06269 55175] Eastwards across the drift-covered country another exposure is laid bare in Glenlaggie, a ravine cut by a tributary of the Garthland Burn about half a mile south-east of Colfin Farmhouse. About 400 yards up this burn the black platy shales, breaking into small sub-angular fragments, dip S. 10°–15° E. Graptolites are not abundant, but the following forms were here collected:
Diplograptus quadrimucronatus (Hall.)
Diplograptus foliaceus
Leptograptus flaccidus (Hall.)
Climacograptus sp.
Dicellograptus sp.
Corynoides calycularis (Nish.)
On the north bank of this stream there is evidence of inverted isoclinal folding of the black shales. On the south bank, at the fossiliferous locality, these black shales pass upwards into gritty greywackes.
Colfin Glen. — [NX 05605 55680] Rather to the north of the strike of the Morroch Bay band, and about half a mile to the north-west of the outcrop in Glenlaggie, black shales appear in Colfin Glen, between Upper Kilhilt and Colfin Farmhouse. They are seen in the bed of the stream, very much shattered, but yielding traces of graptolites. In the field on the south side of the glen, and not far from the stream, black and dark blue shales occur at the base of the steep slope, dipping south-east underneath greywackes and sandy shales. The dark blue shales contain Leptograptus flaccidus, Diplograptus foliaceus, and Dicellograptus. These strata resemble some of the seams belonging to the horizon of the D. quadrimucronatus sub-zone.
Half a mile up the wooded glen [NX 05290 55353], Hartfell Shales again appear, dipping N. 20° W. The shales are platy, and merge into black-blue shales, or dark blue micaceous shales and grits. Some of the bands yield the same assemblage of fossils as noted above, viz.: Leptograptus flaccidus, Diplograptus foliaceus, Dicellograptus, Diplograptus quadrimucronatus, and Cryptograptus tricornis. Greywackes are found between the arches of black shales in this part of the glen.
Portayew Bay. — [NX 03905 50251] About two miles to the south of the important section in Morroch. Bay, the Hartfell black shales rise on a fold in the midst of Barren Mudstones in Portayew Bay. About 100 yards to the south of the centre of this bay, where the Portayew Burn flows into the sea, at the base of the rocky cliff, cleaved black shales containing limestone nodules appear; but notwithstanding- the cleavage, certain layers contain specimens in good preservation of Diplograptus foliaceus, D. quadrintucronatus, Dicellograptus elegans, D. caduceus, D. Forchhammeri, Dicranograptus ramosus, Climacograptus, Obollela, &c. These fossiliferous beds plunge underneath grey shales and mudstones, evidently the equivalents of the Barren Mudstones of Moffat, which contain limestone nodules, and are associated with greywacke bands, the whole series forming a prominent cliff. Northwards, contorted and shattered black shales at the base of the cliff have furnished specimens of Dicellograptus and Climacograptus.
Immediately to the south of the mouth of Portayew Burn [NX 03922 50201] a massive dyke of igneous rock extends from the beach up the cliff along the south bank of the burn. Black shales appear on the cliff to the north of this dyke, much crushed, but containing Didymograptus, Dicranograptus ramosus, Diplograptus Whitfieldi, D. euglyphus, Cryptograptus tricornis, &c. — forms which indicate their Glenkiln horizon. This identification of their stratigraphical position is confirmed by the appearance of the grey radiolarian cherts in association with them while the presence of the Lower Hartfell Shales is indicated by the occurrence of specimens of Diplograptus quadrimucronatus in the same outcrop.
Crailloch Burn. — [NX 03336 59335] About two miles to the south-west of Stranraer, and to the north of the strike of the Morroch Bay band, several exposures of black shales in the midst of pebbly grits and greywackes have yielded graptolites sparingly owing to cleavage. Of these outcrops, the best is to be found in the Crailloch Burn, about a mile- W.N.W. from Piltanton Burn. Greywackes and shales are there laid open, and a few yards south from a stone fence grey mudstones are seen on the west bank of the burn. At the point where this fence crosses the burn, flaky black shales have furnished a few graptolites including Corynoides calycularis in abundance in some seams, Diplograptus foliaceus, Dicellograptus, and Cryptograptus tricornis. These beds dip south-east, and beyond the fence black shales appear with a similar south-east dip. At a bend of the stream, from black shales associated with black flinty ribs of the Glenkiln type the following graptolites have been collected:
Thamnograptus scoticus (Lapw.)
Diplograptus foliaceus (Murch.)
Diplograptus euglyphus (Lapw.)
Cryptograptus tricornis (Carr.)
Dicranograptus ramosus (Hall.)
Dicellograptus Forchhammeri (Gein.)
Dicellograptus sextans (Hall.)
Climacograptus Schärenbergi (Lapw.)
Climacograptus bicornis (Hall.)
Climacograptus caelatus var. antiquus (Lapw.)
A good exposure of grey radiolarian cherts may be seen on the north bank; westwards, however, greywackes, grits, and shales occur, which must be faulted against the black Glenkiln Shales and cherts. Westwards, near the cottage of Greenknowes, thin seams of black shale are intercalated in greywackes and shales, which, though much cleaved, still show traces of graptolites. Further down the stream, on its south bank at a point due north of Crailloch Farmhouse [NX 04089 59160], and about a third of a mile west of Piltanton Bridge, highly bleached black shales appear from which the black colour has disappeared, the outer surface of the shales being stained red, and the interior of a grey or whitish-grey tint. A few yards up the grassy slope on the south side they yield the following graptolites: Dicranograptus, Dicellograptus, Diplograptus foliaceus, Climacograptus, &c. At various places on Crailloch Hill and to the west of Crailloch Farmhouse, black shales and mudstones appear in the midst of greywackes, grits, and shales. They are much cleaved, and only fragments of graptolites have been obtained from them.
Shore-section front Corsewall Lighthouse to Portpatrick
The coast from Corsewall Lighthouse [NW 97992 72690] southwards for twelve miles to Portpatrick [NW 99734 54049] furnishes important evidence regarding the variation in the types of the Llandeilo-Caradoc Rocks from those which prevail in the Moffat series. At various places throughout this section graptolites occur, sometimes in normal black shales and sometimes in thin dark films in grey shales, slates, and greywackes. Owing to the occurrence here of fossils belonging to the Glenkiln and Hartfell divisions, in the dark seams interleaved in coarser sediments, it is extremely difficult to draw a boundary line in this area between the Llandeilo and Caradoc rocks. We will therefore describe the whole series of sediments of Llandeilo-Caradoc age exposed on the coast line southwards from Corsewall Point.
At the northern limit of the section, between Milleur Point [NX 01896 73702], the western headland of Loch Ryan and Corsewall Point [NW 97992 72690] — a remarkable development of coarse conglomerate presents itself, the lithological characters of which were described long ago by Mr. Carrick Moore. The rock is well displayed on the sea-cliffs at the lighthouse, where it contains coarse boulder-beds, between which, the intervening bands are composed of greywacke and sandy shale. The pebbles lie in a matrix of coarse grit in which there are abundant small fragments of red radiolarian chert. The largest and most abundant blocks are composed of acid granitoid rocks, which are associated with pebbles of intrusive basic material, similar to the acid and basic intrusive igneous rocks of the Ballantrae volcanic region. Among the smaller blocks are specimens of diabase and diabase-porphyrite lava, serpentine, quartz-felsite, red chert, limestone, and rarely greywackes and black chert.
Southwards for more than a mile from the lighthouse [NW 97089 71306], the strata of massive grits, which have been stained by overlying rocks now removed by denudation, are varied occasionally by more pebbly bands, but without assuming the character of coarse conglomerates. They are vertical or nearly so, and are traversed by many faults which run north-west and south-east. Beyond the Ox Rocks the grits are succeeded by mudstones and hard ribs, the former being green in fresh fracture and strained red in joints. On the shore opposite the Genoch Rocks [NW 96743 70656], conglomeratic hands reappear, with pebbles, two to three inches across, of rocks similar to those in the conglomerate at the lighthouse, the matrix being mainly made up of igneous material. The general dip of the strata is to the S.S.E. at angles varying from 10°–30°. Still further south, the mudstones and hard bands are again met with, rolling about at comparatively low angles, but with a general inclination to the S.S.E., and they cuntinue as far as Portnaughan Bay [NW 96588 69910], where the beds are smashed and reddened along a line of fault. Beyond this fault the beds still dip southwards, but at the southern headland of the bay they begin to dip to the north at angles varying from 5°–17°. Prom Portnaughan south to Dounan Bay [NW 96586 68862], the same general lithological type continues, consisting of mudstones with hard ribs and sandstone bands.
At Port Long [NW 96364 69010], north of Dolman Bay, the beds are much brecciated, and hematite fills the space between the broken fragments. Again, in the north part of Dolman Bay, they are much shattered and brecciated by faulting. In Port Long — a small cove in this bay — they are traversed by a fault breccia, sometimes fifteen feet broad, which contains hematite. About the middle of Dounan Bay, a powerful fault is seen on the shore, of which the dislocations just referred to are probably oft-shoots, and in which occurs a white clay that was mined about 100 years ago, ruins of the old kiln being still visible. This dislocation is probably the south-west continuation of the Glen App fault, which reappears on the west side of Loch Ryan in Lady Bay. North of Dolman Bay, on the west coast, and again on the shore of Loch Ryan near Lady Bay [NX 02695 71872], the strata have been reddened, probably by staining from the younger red rocks now removed. The hematite vein may be due to this cause.
At the south half of Dounan Bay, a marked change takes place in the character of the strata. They now consist of grey and blue sandy micaceous shales with grey limestone nodules, the latter measuring in some instances several feet across. They are well seen in the bay at low tide: At the south limit of the bay, where the shore road exposes a cliff section of these shales, the dark strains in them have supplied the following forms: Diplograptus foliaceus, Climacograptus bicornis, C. Schärenbergi, Dicellograptus, Dicranograptus ramosus, Diplograptus euglyphus, and a sponge.
Southwards, beyond some grits, flags, and shales, similar shales to those in Dounan Bay appear at a point about 100 yards south of the fossiliferous locality just referred to (Burnfoot on the six-inch map), where they have yielded Dicellograptus divaricatus, Dicellograptus sextans, D. patulosus, Dicranograptus ramosus, Climacograptus bicornis, Climacograptus Schärenbergi, and Diplograptus foliaceus. The fossiliferous shales are usually associated with a pebbly band.
From these shales southwards to Saltpan Bay [NW 96398 67436], the shore presents an alternation of greywackes and shales, together with the Dounan shales. At Castle Butt [NW 96494 67834] some fossils occur in the Dounan shales. Excellent examples of overfolding are seen at March Port [NW 96621 68202], half a mile north of Saltpan Bay, the beds dipping in isoclinal folds to the south. At a point where a burn discharges into the latter bay, rusty flaggy grey shales with black strains appear as a fold in the grits. The shales contain limestone nodules, and in the dark seams poorly preserved graptolites occur, one being Climacograptus like caudatus. The fossiliferous shales are here associated with pebbly grits, like a "Haggis Rock", containing fragments of chert, black shale, and lava. In this bay the beds all dip southwards. The grits are succeeded by sandy argillaceous greywackes, till at a spot, named the Swallow Port on the six-inch map, about 200 yards south of Saltpan Bay, two arches of the Dolman Shales show themselves. For a quarter of a mile down the shore, the greywackes alternate with thin bands of shale, till at Slocknamorrow [NW 96040 66566], 300 yards north of Portobello, the Dounan shales reappear and occupy the bay. Here they have yielded Corynoides calycularis, Dicranograptus ramosus, Dicellograptus moffatensis, Climacograptus bicornis, and Climacograptus caudatus.
North of Portobello [NW 96052 66438] the beach exposes another fold of the Dounan shales, and they reappear on several arches south of the port within a distance of a quarter of a mile, where the evidence of inverted folding is very pronounced. For nearly a mile south of March Port [NW 96014 65913], as far as a bay 500 yards south of Juniper Rock (Broad Port) [NW 95983 64898], greywackes alternate with pebbly grits and thin shaly partings. At Broad Port, however, the Dounan shales reappear and occupy the whole of the bay. Excellent examples of overfolding occur in this, bay, all the over-folds clipping southwards, and there are likewise instances of reversed and normal faults. Limestone nodules are met with, and in the dark strains specimens of Climacograptus bicornis and Corynoides calycularis were collected.
The south horn of Broad Port Bay is occupied by pebbly grits, and further south the Dounan shales with limestone nodules reappear. Fine examples of overfolding are also visible, the overfolds still dipping south. The shales occur again in Slouchnawen Bay [NW 96019 63755] with numerous limestone nodules, and contain Dicranograptus ramosus, Climacograptus bicornis, &c.. The same beds reappear about 200 yards south of the mouth of Galdenoch Burn in Wee Port Bay [NW 95925 63229].
Southwards, seams of greywacke about one foot thick with shale partings occupy the coast. Near Saltpans Bay, Dounan shales, much folded, extend along the shore, nearly all the folds being inverted and dipping south. Nodules of limestone and greywacke occur in the shales. The south part of Saltpans Bay [NW 96530 61495] is occupied by pebbly grits and greywackes, and for nearly a mile to the south the beds consist chiefly of greywackes with some shale bands.
For half a mile south of the mouth of the burn which falls into Broadsea Bay west of Little Larbrax Farmhouse [NW 97408 59661], the rocks consist of sandy greywackes — intermediate in character between mudstones and greywackes — with a lumpy mode of weathering and thin shale partings. Fine overfolding is visible here in the greywackes. Half a mile south of the mouth of the Larbrax Burn in Broadsea Bay, at the mouth of a small stream W.N.W. of Portslogan Farmhouse [NW 98017 58142], a lenticular band of black shales, charged with typical Glenkiln fossils, occurs along the crest of an arch, in the heart of grey-blue shaly- mudstone, followed by grey greywackes on both sides of the isoclinal fold. The beds overlying the black shales are seen to converge up the cliff. The lenticle of black shale is about two feet across at its broadest part. The fossils from it include typical Glenkiln zonal forms,. well preserved and readily identifiable. It may be noted that Caenograptus occurs here in great abundance and in excellent preservation. The species here collected are:
Didymograptus superstes (Lapw.)
Dicranograptus ramosus (Hall.)
Caenograptus gracilis (Hall.)
Dicellograptus sextans (Hall.)
Dicellograptus pertenuis (Lapw.)
Cryptograptus tricornis (Can.)
Cryptograptus surcularis (Hall.)
Climacograptus Schärenbergi (Lapw.)
Diplograptus foliaceus (Murch.)
Diplograptus bicornis (Hall.)
From this point southwards along the coast for a distance of 250 yards, the section presents several features of interest. The Arenig cherts appear on two folds, and there are three exposures of fragmental volcanic rocks associated with the sediments. Beyond the inverted arch of Glenkiln shales just described, the mudstones and greywackes appear, the latter occupying the coast line for a distance of about 100 yards. Thereafter for a distance of 40 or 50 yards the beach is strewn with shingle, and here and there isolaied skerries appear, composed of blue-grey shales and greywackes. In the centre of these skerries are found the fragmental volcanic rocks.
About 170 yards south of the Glenkiln black shales, a prominent narrow ridge, a few feet in breadth, leaves the cliff and runs out to sea in the form of skerries. The largest development of volcanic rocks is here visible. The core of the ridge is composed of these rocks, which are best seen where the materials are worn by the sea. They consist of agglomerates or tuffs and slaggy lavas. The north side shows about six feet of agglomerate, followed by a thin bed of lava, from eight to ten inches or one foot thick, which is in turn succeeded by ten inches of black shales and greywackes. The lava is much deformed, the vesicles are elongated, and the cleavage-planes which traverse the rock dip south at high angles. The agglomerate, which is not deformed, is charged abundantly with blocks of vesicular lava in rounded or bomb-shaped masses. The most abundant blocks in the agglomerate are grey cherts, next come the black shales, and next in order are greywacke fragments. From one fragment of black shale included in this agglomerate the following list of fossils was obtained:
Didymograptus superstes (Lapw.)
Caenograptus gracilis (Hall.)
Caenograptus pertenuis (Lapw.)
Caenograptus surcularis (Hall.)
Dicranograptus minimus (Lapw.)
Dicranograptus ramosus (Hall.)
Dicellograptus sextans (Hall.)
Diplograptus euglyphus (Lapw.)
Diplograptus foliaceus (Murch.)
Cryptograptus tricornis (Carr.)
Glossograptus Hincksi (Hopk.)
Climacograptus bicornis (Hall.)
Dicellograptus sp.
Five yards to the north of the ridge just described the tuff reappears on a knob peering through the shingle, while another exposure is met with still further north in the heart of mudstones. The occurrence of fragments of black shale, containing a characteristic assemblage of Glenkiln graptolites, in the tuff associated with sediments that apparently overlie the adjacent Glenkiln shales to the north, may be regarded as indicating the Lower Caradoc age of this volcanic zone. South of the ridge for a distance of 25 yards, grits project in isolated patches through the gravel, till at the south end of the bay grey and black radiolarian cherts appear, with intercalations of green mudstones. The relations to the rocks on the north side are not visible. On the south side of this fold of cherts a thin band of tuff is to be seen in contact with the cherts, succeeded by dark sandy shales or mudstones containing fragments of chert. This series of rocks is truncated by a fault which brings in grits and greywackes that form the headland south of the bay and occupy about 50 yards of the coast section.
The next core reveals another arch of the cherts, truncated on the south side by a fault which brings in grits. On the north side black shales come in contact with the cherts, which are nodular, grey, and streaked black with stained radiolaria. The first foot of black shales yields typical zonal Glenkiln forms:
Caenograptus gracilis (Hall.)
Caenograptus pertenuis (Lapw.)
Dicranograptus minimus (Lapw.) abundant and well preserved.
Cryptograptus tricornis (Carr.)
Climacograptus bicornis (Hall.)
Diplograptus foliaceus (Murch.)
To the north of this band of black shales, and immediately succeeding it, with an inverted southerly dip, dark sandy shales with black strains, from five to six feet thick, have yielded Climacograptus bicornis.
On the south side of the exposure of cherts, the greywackes brought into contact with them by a fault become pebbly, till at a point 100 yards south of the cherts a massive conglomerate comes in at Dove Cove; two-thirds of a mile north of Knock Bay, composed of boulders of greywacke, calcareous nodules, &c., from six inches to two feet across. The calcareous nodules decompose more readily than the matrix, giving the rock a honeycomb appearance. This conglomerate occupies the coast for a distance of 30 or 40 yards.
From this point along the coast, greywackes and shales are seen, till at the mouth of a burn, a quarter of a mile north of Knock Bay [NW 97946 58199], there is an exposure of cherts and black shales, the cherts occurring three times in the midst of the black shales and greywackes. The beds are much shattered and crushed, and fossils are very difficult to obtain from them. After considerable search, only one thin seam yielded graptolites which included Climacograptus bicornis, together with Dicellograptus, Corynoides calycularis, and Acrotreta Nicholsoni.
In the skerries at low tide, in the strike of some of the beds just described which occur in the cliff, a series of black and grey grits, with lenticles of black shales, is surrounded with grits. These lenticles have yielded Corynoides calycularis, Diplograptus foliaceus, and Climacograptus. A little to the south, in the same bay, another arch shows thin black shales on the cliff that bounds the beach on the south side of the stream. This is followed by greywackes, and about 100 yards south of this point black sandy shales occur, containing Corynoides calycularis in great abundance, Climacograptus, and Dicellograptus. From Knock Bay [NW 98206 57659] to the south of Kilintringan Bay [NW 98207 56843] the shore displays a succession of greywackes and shales with black strains yielding graptolites. In Kilintringan Bay the grey and blue shales with dark strains appear in force, the latter yielding Climacograptus bicornis and Cryptograptus tricornis .
From the foregoing description of the strata exposed on the shore between Corsewall Lighthouse and Kilintringan Bay, north of Portpatrick, it is clear (1) that the radiolarian cherts of Arenig age are exposed on anticlinal folds as far north as Broadsea Bay; (2) that at the same locality the typical Glenkiln graptolites still occur in a normal black shale, followed by sediments which contain thin dark seams yielding graptolites common both to the Glenkiln and Hartfell groups; (3) that between Broadsea Bay and Corsewall Point there is a constant repetition of blue and grey shales with dark fossiliferous seams, sandy greywackes, pebbly grits, mudstones, and shales, which may belong partly to the Glenkiln series (Llandeilo) and partly to the Hartfell (Caradoc). The assemblage of graptolites is such that no very definite opinion can be pronounced as to the relative age of the various sediments.
We will now proceed to adduce evidence that inland, by Cairn Ryan and Barrhill, to Craiglure Lodge near Loch Dolan, the Glenkiln assemblage of graptolites occurs in thin dark films or seams interleaved in shales, slates, and greywackes.
Cairn Ryan District. — [NX 06273 68621]This part of Wigtownshire affords proof that the fossils characteristic of the Glenkiln division no longer occur in shales of the central Moffat type. Certain zonal forms confined to the Glenkiln horizon are there found in dark seams interleaved in grey and blue slates and shales. One of the best examples is to be found in the Cairn Ryan Slate Quarries [NX 06801 68812]— a locality long known through the discoveries of Carrick Moore. Here grey and blue slates contain thin dark seams yielding Didymograptus superstes, Climacograptus, Diplograptus, and Dicellograptus. The fossils are confined to these dark seams, and are not in good preservation. Similar evidence is obtained on the east shore of Loch Ryan, near Polymodie Burn [NX 05898 70312], which joins the sea about a mile and a quarter north of Cairn Ryan. About 20 yards south of the mouth of this burn, the following fossils were collected from dark strains in grey shales intercalated in grits:
Didymograptus superstes (Lapw.)
Lasiograptus bimucronatus (Nich.)
Diplograptus foliaceus (Murch.)
Cryptograptus tricornis (Carr.)
Climacograptus sp.
Dicellograptus sextans (Hall.)
Dicellograptus patulosus (Lapw.)
Dicranograptus ramosus (Hall.)
Again, about 50 yards north of the mouth of Polymodie Burn, the following assemblage was obtained:
Diplograptus foliaceus (Murch.)
Diplograptus euglyphus (Lapw.)
Lasiograptus bimucronatus (Nich.)
Climacograptus celatus var. antiquus (Lapw.)
Cryptograptus tricornis (Carr.)
Dicellograptus sextans (Hall.)
Dicellograptus patulosus (Lapw.)
Dicellograptus like flexuosus (Lapw.)
Northwards, the shore of Loch Ryan to the mouth of Glen App [NX 05041 72708] displays a constant repetition of grey and blue shales and greywackes, having a general dip to the south-east at high angles (Sheet 7 of the Survey Map). At the roadside at the mouth of Glen App, the graptolites given in the annexed list were collected from dark seams in grey shales or slates:
Diplograptus euglyphus (Lapw.)
Diplograptus foliaceus (Murch.)
Climacograptus bicornis (Hall.)
Climacograptus peltifer (Lapw.)
Similar evidence is obtained in the district-of Barrhill [NX 23465 82183] (southwest corner of Sheet 8), where a great development of grey shales with occasional greywacke bands, though resembling lithologically the Lowther Shales (Caradoc), yet in certain dark sandy seams furnish a characteristic assemblage of Glenkiln graptolites. This shaly group is well exposed in Feoch Burn [NX 25024 81399] and Cross Water [NX 25024 81399], both tributaries of the river Duisk, and also in the Laggish Burn [NX 22231 78264] — an affluent of the Pollgowan Burn — the general inclination of the strata being to the south-east at high angles. Excellent fossiliferous localities occur in the Cross Water, which joins the Duisk River from the south-west at the village of Barrhill. In this section, at a point above the Linn Dubh [NX 22864 81166], three-quarters of a mile south-west of Barrhill, and 400 yards S.S.E. of Ward, dark micaceous sandy shales, weathering with a rusty coating on the joints, have furnished the following fossils:
Didymograptus superstes (Lapw.)
Caenograptus gracilis (Hall.)
Caenograptus pertenuis (Lapw.)
Diplograptus euglyphus (Lapw.)
Diplograptus Whitfieldi (Hall.)
Diplograptus foliaceus (Murch.)
Cryptograptus tricornis (Carr.)
Lasiograptus bimucronatus (Hall.)
Dicellograptus moffatensis (Carr.)
Dicellograptus divaricatus (Hall.)
Dicellograptus sextans (Hall.)
Dicellograptus sp.
Dicellograptus patulosus (Lapw.)
Dicranograptus ramosus (Hall.)
Climacograptus bicornis (Hall.)
Climacograptus caelatus var. antiquus (Lapw.)
ClimacograptusSchärenbergi (Lapw.)
Leptograptus flaccidus (Hall.)
Siphonotreta micula (M'Coy.)
On the south bank of this stream, opposite the spot where the foregoing list of graptolites was collected, grey mudstones with leaf-like black seams and greywackes occur, the dark seams yielding zonal forms of the Glenkiln division. About 300 yards further up the section, near a small linn, grits and shales with dark strains are exposed, the sequence of beds differing lithologically from those just referred to, which furnish the typical Glenkiln graptolites. Yet the dark seams afforded the following zonal Glenkiln forms:
Caenograptus gracilis (Hall.)
Lasiograptus bimucronatus (Nich.)
Dicellograptus sextans (Hall.)
Dicranograptus ramosus (Hall.)
Climacograptus bicornis (Hall.)
Diplograptus euglyphus (Lapw.)
Diplograptus perexcavatus (Lapw.)
Cryptograptus tricornis (Carr.)
Corynoides calycularis (Nich.)
The Cross Water, from the Linn Dubh to the village of Barrhill [NX 23205 81778], flows over a constant repetition of grey shales with black strains and greywackes, the dark seams yielding various zonal Glenkiln forms, including Caenograptus gracilis, Lasiograptus bimucronatus, Dicellograptus sextans, Diplograptus euglyphus. Similar fossiliferous bands were observed in the river Duisk opposite Blair Farmhouse [NX 24436 81537], and in the Feoch Burn, near Laggan Wood [NX 25261 81932], one mile east of Barrhill village, and again near the head of Laggish Burn, north of Chirmorie [NX 21054 77578] approx.
From the evidence now brought forward, it is apparent that in the Barrhill district the Glenkiln division of the Moffat region (Upper Llandeilo) must be represented by grits, greywackes, and shales associated with thin fossiliferous seams yielding Glenkiln graptolites; for though there is undoubtedly much reduplication of the strata, it is obvious that the sections cannot be explained by the repetition of only one thin seam charged with Glenkiln forms. Throughout the Barrhill district the Arenig cherts have not been met with; they do not appear for three miles to the north-west of that village, where, in the valley of the Muck Water, they are associated with Arenig lavas.
Kirriemore Burn, Minnoch Water (Sheet 8). — In the basin of the Minnoch Water, in the Kirriemore Burn, east of Kirriereoch Loch [NX 37590 86619], black shales and thin dark seams alternate with grey shales and grits, which have been traced south-westwards to the Minnoch and north-eastwards to the Cross Burn, south of Tarfessock Hill. Perhaps the best sections are those in the Kirriemore Burn, where the strata are repeated by folds, and where one or two fossiliferous localities have been recorded. Graptolites are not readily obtained in the more platy black shales with iron pyrites. In the bank of this burn, about a mile east of Kirriereoch Loch, the black shales dip S.S.E. at 78°, and have yielded the following fossils:
Didymograptus superstes (Lapw.)
Lasiograptus bimucronatus (Nich.)
Dicellograptus sextans (Hall.)
Dicellograptus flexuosus (Lapw.)
Dicellograptus patulosus (Lapw.)
Diplograptus euglyphus (Lapw.)
Diplograptus foliaceus (Murch.)
Diplograptus perexcavatus (Lapw.)
Glossograptus Hincksi (Hopk.)
Leptograptus flaccidus (Hall.)
Dicranograptus minimus (Lapw.)
Dicranograptus ramosus (Hall.)
Dicranograptus formosus (Hopk.)
Cryptograptus tricornis (Carr.)
Climacograptus bicornis (Hall.)
Climacograptus peltifer (Lapw.)
Brachiopod.
Further down the burn, within half a mile of Kirriereoch Loch [NX 37132 86426], where grey shales alternate with black seams embedded in grits, Cryptograptus tricornis, Climacograptus bicornis, Diplograptus foliaceus were collected.
Craiglure Old Lodge (Head of Girvan Water). — [NX 42113 96962] When we pass northwards to the area situated between the northwest margin of the Loch Doon granite and the great fault which brings the Lower Old Red Sandstone against the Silurian rocks, we obtain confirmatory evidence of the intercalation of the Glenkiln fauna in coarse sedimentary deposits. Various exposures of blue or grey shales with dark reams interbedded with massive grits and greywackes are met with near Loch Lure [NX 41982 97179], which can be followed westwards for two miles to the river Stinchar. A glance at the Geological Map (Sheet 8) will show the positions of several outcrops of these fossiliferous shales in that region. One of the best fossiliferous localities is in an old slate quarry by the roadside, near the ruins of Craiglure Old Lodge, where dark blue shales, dipping S.S.E. at high angles, have yielded the following assemblage of graptolites:
Didymograptus.
Caenograptus gracilis (Hall.)
Caenograptus pertenuis (Lapw.)
Caenograptus nitidiulus (Lapw.)
Dicellograptus moffatensis (Carr.)
Dicellograptus divaricatus (Hall.)
Dicellograptus sextans (Hall.)
Dicellograptus patulosus (Lapw.)
Climacograptus bicornis (Hall.)
Climacograptus tridentatus (Lapw.)
Climacograptus Schärenbergi (Lapw.)
Diplograptus euglyphus (Lapw.)
Diplograptus foliaceus (Murch.)
Dicranograptus ramosus (Hall.)
Cryptograptus tricornis (Carr.)
Leptograptus capillaris (Carr.)
Hyalostelia faseiculus (M'Coy.)
Again, on the banks of the river Stinchar, not far to the south of Craiglure new lodge [NX 39855 95120], similar dark blue shales have furnished the graptolites given in the annexed list:
Caenograptus pertenuis (Lapw.)
Dicellograptus sextans (Hall.)
Dicellograptus patutosus (Lapw.)
Climacograptus bicornis (Hall.)
Diplograptus euglyphus (Lapw.)
Diplograptus foliaceus (Murch.)
Diplograptus mucronatus (Hall.)
Cryptograptus tricornis (Carr.)
Glossograptus Hincksi (Hopk.)
The strata throughout the area surrounding Loch Lure are isoclinally folded, the general dip of the strata being southeasterly.
Sediments of Caradoc Age overlying the Glenkiln–Hartfell Shales to the North of the Llandovery Area in Wigtownshire and the Western part of Kirkcudbrightshire
In the region lying to the north of the Llandovery boundary line in the county of Wigtown and the western part of Kirkcudbrightshire, certain sediments may with considerable probability be referred to the Caradoc formation. The evidence adduced in the forgoing pages leads to the conclusion that along the strike of the Curleywee, Glassoch, and Gabsnout band of black shales (pp. 387–395), the Diplograptus quadrimucronatus zone (Lower Caradoc) of the Harden black shales is represented, and that on the strike of the Tannylaggie and Glen Trool band the Climacograptus caudatus sub-zone (Lower Caradoc) has been recorded. It is therefore fair to infer that the coarse sediments which occupy the synclinal folds between these outcrops may be of Caradoc age.
Along the south side of the Morroch Bay, Gabsnout, and Curleywee bands of black shale a prominent zone of shales, with greywackes and occasional pebbly grits, is regarded as the representative of the Barren Mudstones of the Moffat area. The only localities where the Moffat black shales have been noted as appearing in the midst of these grey shales between the Cree and Water of Luce are (1) at Glenhowl, south-east of Camrie [NX 20829 59288], and (2) between Glassoch and the Cree. The rocks immediately in contact with the black shale bands between Gabsnout, Glassoch, and Cardorkin generally consist of greywackes or grits, followed by grey shales. Those which succeed the Tannylaggie black shales on the south side are composed of grey shales with dark strains, succeeded by grey rusty irregularly-jointed greywackes, with partings of grey and blue micaceous shales. A feature in this series is the occurrence of a band of fine conglomerate or pebbly grit, the pebbles in which range from the size of a pea to two or three inches in length, and consist of quartz, black and grey shales, chert, and greywacke. The rock is sparingly fossiliferous, fragments of Ptilodictya, Petraia, Heliolites, and crinoid stems having been obtained from the exposures near the Snaip [NX 31354 71407] and from the head of the burn a mile and a half north of Glassoch. This fossiliferous grit is well seen on the north bank of the river Bladenoch, about half a mile south-west of the Snaip [NX 30675 70742], whence it can be traced north-eastwards to the Cree. South-westwards it has been observed on Eldrig Fell and Balmurrie Fell (north-west corner of Sheet 4).
In the belt of sediments extending from the Tannylaggie black shales to the Drumabrennan outcrop (p. 397) — a distance of 2½ miles — the Moffat Shales come to the surface along an axial fold in a tributary of the Bladenoch about a mile and a half S.S.E. of Snaip [NX 31793 68974]?. It is probable, therefore, that no great thickness of sediments overlies the Glenkiln–Hartfell Shales in the northwestern part of Sheet 4.
As regards the area between the Glen Trool, Tannylaggie, and New Luce black shale bands on the south, and the valleys of Glen App and Glen Muck on the north, it would be obviously unsafe in the present state of our knowledge to indicate the relative age of the coarse sediments associated with the black shales. Owing to the disappearance throughout that region of the zonal Hartfell graptolites and the intimate, association of the Glenkiln forms with shales, greywackes, and pebbly grits, it is probable that a large part of these coarse sediments may be of Upper Llandeilo age, and that some portion may be of Caradoc age. To the north of Glen App and Glen Muck, however, the Arenig lavas, radiolarian cherts appear together with blue-black mudstones which are charged with typical Glenkiln graptolites.