Chapter 12 II. The Northern Belt. Arenig, Llandeilo, and Caradoc Formations in the district between Abington and Eddleston

We have now to consider the nature, development, and tectonic arrangement of the Silurian rocks which extend along what we have termed the Northern Belt of the Southern Uplands — that is, the long strip of ground which extends from the northern slopes of the Lammermuir Hills south-westwards through the Moorfoot and Leadhills across Upper Nithsdale and Carrick to the western coast of Loch Ryan and Portpatrick.

In order to show, in the first place, the relation of the volcanic rocks at the base of the Lower Silurian series to the radiolarian cherts and overlying black shales, we shall begin with certain typical sections where the sequence can be established. Some sections show the relations of the lavas and agglomerates to the cherts, others reveal the succession from the radiolarian cherts to the Climacograptus caudatus zone of the Hartfell black shales.

Basin of the Wandel Water

About three miles to the north of Abington the Clyde receives an important tributary — the Wandel Water — which drains the high ground forming the watershed between the Clyde, the Tweed, and the Culter Water. The streams uniting to form the Wandel Water display more or less continuous sections of the volcanic series and the overlying sediments.

Hawkwood Burn. — One of the clearest sections is met with in the Hawkwood Burn ((Figure 42), (Figure 43)), which joins the Wandel Water about 300 yards to the north of Birnock shepherd's house (north-east corner of Sheet 15 of the Survey Map). At the head of this stream, about three-quarters of a mile above its junction with the Wandel Water [NS 97108 24703], and close to the heath-clad watershed between the Rome and Tewsgill Hills, the volcanic rocks occur in the midst of the cherts. On the west slope of the hollow cut out by this stream the rocks are comparatively bare and the sequence on the north side of the anticline is quite visible. In the centre of the fold lies a mass of volcanic agglomerate (1 Ts), dipping at a very high angle to the N.N.W. The breadth of the exposure, measured across the arch, a few yards up the west bank, is 26 feet; so that the actual thickness of the agglomerate here is 13 feet. The matrix, dirty green in colour and highly decomposed, is made up apparently of finely divided igneous detritus, in which lie the volcanic blocks. The latter, sometimes rounded and sometimes elongated in form, and varying in size from one to several inches in diameter, consist chiefly of vesicular diabase.

On the north side the agglomerate is visibly overlain by the red cherts (C), their breadth of outcrop measuring 45 feet, followed by the grey chert zone, with shales and mudstones covering a horizontal distance of 96 feet. Here this sub-division is evidently repeated by folds, for in other sections the measurements give a smaller thickness. Beyond the grey cherts, in a small scar on the west slope, some black shales yield fragments of Glenkiln forms in very poor preservation, and are abruptly truncated by a fault (f),bringing them into contact with greywackes and shales.

In the south limb of the fold the red cherts are seen in contact with the agglomerate, succeeded by red mudstones, but the grey cherts are buried underneath rock debris and vegetation. Beyond the covered area the black slates again appear with ill-preserved Glenkiln graptolites. On the east bank of the stream the agglomerate is exposed, evidently passing underneath the overlying cherts.

In the lower portion of this burn the radiolarian cherts and black shales appear in several folds among the shales, greywackes, and grits. In the sandy shales associated with the greywackes specimens of Diplograptus foliaceus have been obtained.

Back Grain, Ragged Gill. — [NS 97976 24715], [NS 98343 25235]  A confirmatory section, showing the relation of the volcanic rocks to the overlying sediments, occurs in a streamlet on the north slope of Rome Hill, draining into the Ragged Gill — a tributary of the Wandel Water (Sheet 15 of the Survey Map). About 500 yards above its junction with the Ragged Gill, the Back Grain branches into two small streams. In the north branch, slaggy diabase-lava can be followed a short distance up the scar. Here a thin band of black shale, which has as yet proved unfossiliferous, immediately overlies the lava on both sides of the fold. Next in order come the various sub-zones of the radiolarian cherts, followed by the Glenkiln black shales with their characteristic fossils, forming the tops of the cliffs on both sides of the arch. Near the head of the streamlet the anti dine "noses out", and the overlying cherts form the crest of the fold. Towards the south the black shales are repeated by isoclinal folds, and the radiolarian cherts once more appear on another fold; while on the north, the diabase lava is exposed on another anticline. The evidence in this section plainly shows the infraposition of the diabase-lava with reference to the radiolarian cherts and black shales.

Rough Gill. — The sequence from the volcanic rocks into the Glenkiln–Hartfell black shales is further displayed in the Rough Gill, a streamlet joining the Birnock Burn in the extreme northwest corner of Sheet 16 of the Survey Map. Here three streams unite to form the Wandel Water, the Rough Gill [NS 99662 26348], the streamlet draining a rocky hollow named the Deil's Barn Door [NS 99845 26144], and the Birnock Burn [NS 99744 25830]. The first of these, lying furthest north, has, in the upper part of its course, cut a ragged gorge through the rocks now under consideration (Figure 44). There the lava, an aphanitic diabase or altered basalt, is well exposed on the left bank of the stream forming the core of the arch (1 B). From an examination made by Dr. Hatch, this Rock shows, under the microscope, a plexus of small lath-shaped felspars, the interstices of which are filled by alteration products (chlorite, calcite, &c.). The augite is completely decomposed, and there are a few small amygdules of calcite.

Towards the east end of the fold the breadth of the exposure of diabase is 48 feet. On the south side it is truncated by a small fault, with a downthrow to the south, bringing in a higher sub-zone of the cherts (C) with the overlying black shales. In the north-west limb the red cherts, decomposing in part, immediately overlie the diabase-lava succeeded by the higher zones. Here the red cherts measure 30 feet and the grey cherts 42 feet in thickness; giving a total thickness of 72 feet for the radiolarian cherts and mudstones.

The black shales overlying the cherts in this section have Yielded the following forms, characteristic of the Glenkiln horizon:

Didymograptus superstes (Lapw.)

Caenograptus gracilis (Hall.)

Lasiograptus bimucronatus (Nich.)

Lasiograptus Harknessi (Nich.)

Climacograptus bicornis (Hall.)

Dicellograptus sextans (Hall.)

Corynaides sp.

About 300 yards to the south of the gorge known as the Deil's Barn Door this band of black shale is exposed in a highly convoluted form. In the lower part of the scar, near its junction with the Birnock Burn [NS 99625 26039], the radiolarian cherts rise from underneath the black shales. Here the latter are fairly fossiliferous, and their organisms rather well preserved. It is important to note also that in this section specimens of Climacograptus caudatus have been obtained in abundance — a form confined exclusively to the Lower Hartfell Shales, and indicating a Lower Caradoc horizon. The following fossils were obtained from some of the zones in this gorge:

Diplograptus angustifolius (Hall.)

Dicranograptus ramosus (Hall.)

Dicranograptus Nicholsoni (Hopk.)

Climacograptus bicornis (Hall.)

Corynoides calycularis (Nich.)

Retiolites (Neurograptus) fibratus? (Lapw.)

Climacograptus caudatus (Lapw.)

Acrotreta Nicholsoni (Dav.)

This assemblage clearly proves that some of the higher seams in this band belong to the base of the Lower Hartfell black shales.

In the north-west corner of Sheet 16 of the Map, two streams, the Birnock Burn [NS 99726 25821] and the Deer Gill [NS 99157 25355], running parallel with each other to join the Wandel Water, drain the northern slope of the watershed, while a third stream, the Lead Burn [NS 98515 25248], also flows in the same direction. These three burns show transverse sections of the strata, the lowest beds exposed being the radiolarian cherts, followed by the Glenkiln–Hartfell black shales and the succeeding shales and greywackes. The probable prolongations of the same outcrops are indicated, though in such a highly convoluted area, where the folds die out so rapidly, the correlation of anticlines in different streams is a matter of uncertainty. These stream-sections show very clearly the extraordinary reduplication of the strata, and how a very limited thickness of beds may cover a broad area.

The Lead Burn has a fall of 500 feet in three-quarters of a mile (Figure 45) [NS 98515 25248]. At the mouth of the stream the rocks are buried under boulder clay; but about 300 feet higher up the cherts appear. Here their upper bands are particularly massive, insomuch that they have been used for building dykes. About 500 yards from the foot of the stream a massive band of black shales occurs (Glenkiln–Hartfell), which, after being succeeded by greywackes and shales, again emerges further up, but owing to inversion it appears to overlie the greywackes. Beyond this point the cherts and black shales alternate, till at the 1250-feet contour line they are followed by the greywackes and shales, dipping at steep angles to the north. The latter must be folded rapidly on themselves, for at least two anticlines of black shale with the underlying cherts can be traced from the Sowen Hill, along the watershed in the strike of these greywackes and shales.

In the Deer Gill [NS 99157 25355] no rock is exposed for about 150 yards up stream until the cherts appear, and for a distance of 400 yards are constantly repeated by the folds, which are well seen on the banks. About 600 yards from the foot of the burn the Glenkiln–Hartfell black shales succeed, with a S.S.E. dip, and plunge underneath the overlying grey shales and greywackes. Beyond this point the black shales reappear in several folds, one of which reveals the underlying cherts.

At the foot of the Birnock Burn [NS 99579 26009], and just above the point where it is joined by the Rough Gill, the Glenkiln–Hartfell black shales make their appearance, while the radiolarian cherts are visible a few yards off on the south-west bank. Here the following fossils have been obtained:

Didymograptus superstes (Lapw.)

Dicranograptus ramosus (Hall.)

Dicellograptus sextans (Hall.)

Dicellograptus patulosus (Lapw.)

Diplograptus foliaceus (Murch.)

Climacograptus bicornis (Hall.)

Climacograptus caudatus (Lapw.)

The outcrop of this band is much in the same line of strike as that in the Deil's Barn Door, where, as already indicated, Climacograptus caudatus also occurs.

Descending the Wandel Burn to a point about 200 yards above its junction with the Deer Gill [NS 99108 25757], we again come upon the black shales on the north bank of the stream, where they have yielded the fossils enumerated in the accompanying list:

Diplograptus angustifolius (Hall.)

Diplograptus mucronatus (Hall.)

Dicranograptus ramosus (Hall.)

Climacograptus sp.

Hyalostelia fasciculus (M'Coy.)

The same outcrop of black shale can be followed along the north bank to the mouth of the Deer Gill, where the beds are inclined to the N.N.W., and the radiolarian cherts succeed on the north side with an inverted dip. This exposure has given the following assemblage of Glenkiln–Hartfell fossils:

Diplograptus mucronatus (Hall.)

Diplograptus angustifolius (Hall.)

Diplograptus foliaceus (Murch.)

Climacograptus caelatus (Lapw.)

Climacograptus bicornis (Hall.)

Lasiograptus bimucronatus (Nich.)

Cryptograptus tricornis (Carr.)

Dicranograptus ramosus (Hall.)

Amphigraptus sp.

Corynoides calycularis (Nich.)

Acrotreta Nicholsoni (Dav.)

Hyalostelia fasciculus (M'Coy.)

On the south bank of the Wandel Burn, just above the mouth of the Deer Gill, a thin seam of black shale, containing small Diplograpti in great numbers, occurs among greywackes and shales.

Rein Gill. — [NS 98025 25752] At a point about a third of a mile above the shepherd's house at Birnock, the Wandel Burn receives from the north a small tributary named the Rein Gill (Sheet 15). The section exposed in the lower part of this gill is of importance, from the abundance and good preservation of the fossils. Owing to the highly convoluted and shattered condition of the black shales in this northern area, it is often difficult to get a good assemblage of fossils to prove their horizon, and even more difficult to sub-divide them into sub-zones. From this exposure, however, a large collection has been obtained, which has been equalled in this district only by the fine assemblage from the outcrops at the foot of Hawkwood Burn to be described presently. These organisms are given in the following list:

Didymograptus superstes (Lapw.)

Caenograptus gracilis (Hall.)

Caenograptus pertenuis (Lapw.)

Caenograptus nitidulus (Lapw.)

Dicranograptus formosus (Hopk.)

Dicranograptus zic-zac (Lapw.)

Dicranograptus ramosus (Hall.)

Dicranograptus Nicholsoni (Hopk.)

Dicellograptus patulosus (Lapw.)

Dicellograptus var. B. (Lapw.)

Dicellograptus sextans (Hall.)

Dicellograptus intortus (Lapw.)

Dicellograptus elegans (Carr.)

Dicellograptus moffatensis (Carr.)

Climacograptus bicornis (Hall.)

Climacograptus peltifer (Lapw.)

Climacograptus tridentatus (Lapw.)

Cryptograptus tricornis (Carr.)

Diplograptus angustifolius (Hall.)

Diplograptus foliaceus (Murch.)

Diplograptus euglyphus (Lapw.)

Diplograptus perexcavatus (Lapw.)

Lasiograptus margaritatus (Lapw.)

Lasiograptus Harknessi (Nich.)

Lasiograptus bimucronatus (Nich.)

Glossograptus Hincksi (Hopk.)

Acrotreta Nicholsoni (Dav.)

Acrothele granulata (Linn.)

Hyalostelia fasciculus (M'Coy.)

From this list it is apparent that the band of shale at the foot of the Rein Gill contains some forms exclusively confined to the Glenkiln Shales of the Moffat area, and some which occur in that division and part of the Lower Hartfell Shales. From the abundance of the form Dicranograptus ramosus in one of the seams it would almost appear as if the passage beds between the Glenkiln and Hartfell divisions were represented. Climacograptus bicornis and its varieties are particularly abundant and well preserved in this section.

The black shales containing this assemblage of fossils are the first rocks met with in the ascent of the stream. The locality is about 100 yards from the junction of the Rein Gill with the Wandel Water. The beds occur on the north bank and also in the channel of the burn, where, with an inverted dip, they plunge underneath the radiolarian cherts. Proceeding up the burn the observer crosses the charts and finds another outcrop of the black shales yielding Diplograptus angustifolius, D. foliaceus, Cryptograptus tricornis, Acrotreta Nicholsoni, Hyalostelia fasciculus.

Wandel Water. — [NS 97716 25665] In this stream, about 200 yards below its junction with the Rein Gill, the radiolarian cherts and associated black shales again appear. From some of the seams in the latter, specimens have been obtained of Diplograptus angustifolius, Dicranograptus ramosus, Climacograptus bicornis, Corynoides calycularis. At the point where the Wandel Water is joined by the Hawkwood Burn an excellent exposure of the Glenkiln black shales supplies graptolites in profusion and in great variety. No less than seven genera, including eleven species, were counted on one small slab. The shales are finely banded, and split into thin laminae under the hammer. On the south side they are in immediate contact with the greywackes and shales, but to the north the succeeding strata are obscured. The subjoined list enumerates the organisms obtained at this locality

Didymograptus superstes (Lapw.)

Didymograptus serratulus (Hall.)

Thamnograptus typus (Hall.)

Caenograptus gracilis (Hall.)

Caenograptus pertenuis (Lapw.)

Caenograptus explanatus (Lapw.)

Caenograptus nitidulus (Lapw.)

Dicranograptus formosus (Hopk.)

Dicranograptus zic-zac (Lapw.)

Dicranograptus ramosus (Hall.)

Dicranograptus Nicholsoni (Hopk.)

Glossograptus Hincksi (Hopk.)

Lasiograptus margaritatus (Lapw.)

Lasiograptus bimucronatus (Nich.)

Dicellograptus patulosus (Lapw.)

Dicellograptus patulosus var. B. (Lapw.)

Dicellograptus moffatensis (Carr.)

Dicellograptus divaricatus (Hall.)

Dicellograptus sextans (Hall.)

Dicellograptus intortus (Lapw.)

Cryptograptus tricornis (Carr.)

Diplograptus mucronatus (Hall.)

Diplograptus mucronatus very large form.

Diplograptus perexcavatus (Lapw.)

Climacograptus bicornis (Hall.)

Climacograptus peltifer (Lapw.)

Climacograptus tridentatus (Lapw.)

Acrotreta Nicholsoni (Dav.)

At this locality Didymograptus superstes is especially abundant, as well as Cryptograptus tricornis. It is deserving of note that the typical Lower Hartfell graptolite Climacograptus caudatus, which, as already indicated, occurs in the black shales at the Deil's Barn Door, at the head of the Wandel Water, has not been found in this section, though the succeeding greywackes and shales are visibly in contact. It is not improbable that this fold of the black shales lies to the north of the limit of the typical Lower Hartfell graptolites; though some of the forms found at the foot of Rein Gill not far to the south still indicate an assemblage commonly associated with the lower zones of the Lower Hartfell black shales.

Wallace's Cast, Wandel Water. — [NS 96862 26283] Having now described the sequence of strata from the Arenig volcanic rocks and overlying radiolarian cherts to the Glenkiln–Hartfell black shales, we shall refer to the sediments which succeed these graptolite-bearing bands.

Attention has already been directed to the occurrence of Diplograptus foliaceus in grey sandy shales associated with the greywackes near the foot of the Hawkwood Burn, opposite the shepherd's house at Birnock. The section in the Wandel Water to the north of the outcrop of black shales at the foot of Hawkwood Burn is of special interest from the occurrence of a highly fossiliferous zone in the ordinary sediments, at Wallace's Cast (Sheet 15 of the Map). At a distance of 300 yards north from the foot of Hawkwood Burn, on the east bank, brown shales are visible, and after another short break in the section the fossiliferous zone is met with on the same side of the stream. This important band consists of fine grey shale, containing calcareous nodules and lenticular masses of pebbly grit. The fossils occur chiefly in the limestone nodules, which decompose readily by weathering; some are found in the shales and some in the pebbly grit. The limestone nodules are not derivative. Now, though no continuous visible section reveals the relations of this bed to the Glenkiln black shale, there cannot be any doubt that these fossiliferous sediments overlie the Glenkiln beds. The accompanying generalised section (Figure 46) from Rome Hill, across the basin of the Wandel Water to Wallace's Cast, shows the relative position of the various sub-divisions of the Llandeilo–Bala Rocks. The following list of fossils shows that the strata at Wallace's Cast are referable to the Bala or Caradoc formation. Indeed, it is highly probable that part of the Lower Hartfell black shales is there represented. The fossils are chiefly casts, but they are in fair preservation and easily determinable:

Nidulites favus (Salter.)

Petraia bina (Lonsd.)

Lindstromia (Petraia) subduplicata (M'Coy.)

Stenopora (Favosites) fibrosa (Goldf.)

Glyptocrinus basalis (M'Coy.)

Encrinurus punctatus (Briinn.)

Phacops Brongniarti (Portl.)

Illaenus latus (M'Coy.)

Remopleurides laterispirifer (Portl.)

Lingula attenuata (Sow.)

Orthis calligramma (Dalm.)

Orthis (Dalmanella) elegantula (Dalm.)

Orthis (Dalmanella) testudinaria (Dalm.)

Orthis vespertilio (Sow.)

Strophomena corrugatella (Dav.)

Strophomena (Rafinesquina) deltoidea var. rotundata (Conrad.)

Strophomena grandis (Sow.)

Strophomena (Orthis) kilbuchoensis (Dav.)

Strophomena rhomboidalis (Wilck.)

Leptaena sericea (Sow.)

Leptaena sericea var. rhombica (M'Coy.)

Leptaena (Christiania) tenuicincta (M'Coy.)

Leptaena transversalis (Wahl.)

Rhychonella Stricklandii (Sow.)

Rhychonella borealis (?) (Schl.)

Pleurotomaria (Raphistoma) elliptica (His.)

Pleurotomaria lenticularis (Sow.)

Pleurotomaria alata (Wahl.)

Murchisonia gyrogonia (M'Coy.)

Maclurea macromphala (M'Coy.)

Bellerophon acutus (Sow.)

Bellerophon dilatatus (Sow.)

Conularia elongata (Portl.)

Pterotheca corrugata (Salter.)

To the north of the outcrop of fossiliferous shale and grit at Wallace's Cast, grey shales with occasional greywackes are repeated by isoclinal folds.

Abington district east of the Clyde

In the Abington district [NS 93122 23429] lying to the south-west of the basin of the Wandel Water, and to the east of the river Clyde, the Arenig lavas and overlying Llandeilo Rocks are exposed in various folds. To the east of the village of Abington, the Raggen Gill, which flows towards the Clyde and drains the slopes of the Tewsgill and Arbory Hills, displays a section of the volcanic zone and overlying sediments. In this stream the radiolarian cherts are exposed at the bend about half a mile above the railway to the south of Arbory Hill. Traced up the water-course they seem to be repeated by folds, but within a short distance debris of black shales is found on the north bank, with fragments of graptolites, indicating the position of the Glenkiln band. Towards the south, radiolarian cherts again appear, with greywacke probably lying in a fold, but eventually they give place to the volcanic zone, represented here by compact diabase or altered basalt. Under the microscope the rock shows plagioclase felspar in small lath-shaped crystals, brown augite in granular and ophitic masses, with serpentinous pseudomorphs after olivine. It occurs in several folds with intervening cherts, but towards the upper limit of the section the radiolarian cherts are succeeded by a band of black shale and greywackes and shales (Figure 47). The general dip of the strata in this section being towards the north-west, the folding is isoclinal. Unfortunately the black shales are so shattered that it is impossible to prove their horizon satisfactorily by fossil evidence. The only forms obtained are Diplograptus angustifolius, Climacograptus, Acrotreta Nicholsoni. At the northern limit of the section, on Arbory Hill, grey grits occur, which are supposed to be on the same horizon as the fossiliferous grits of Duntercleuch, Lead Hills (Figure 47).

Coldchapel Burn. — [NS 96019 24776] In the Coldchapel Burn, which joins the Clyde about a mile north of Abington, several folds lay bare the radiolarian cherts and black shales. At the bend about a mile and a half above the foot of the stream, the black shales have yielded Diplograptus perexcavatus, C. bicornis var. peltifer, Diplograptus mucronatus, Dicranograptus ramosus, Acrotreta Nicholsoni.

Southwood Burn. — [NS 93921 22888] On the hill slope east of Abington House, the south-west prolongations of the folds reveal the lavas and cherts near the head of Raggen Gill and Coldchapel Burn just described. Here two small burns unite to join the Clyde opposite Abington House. One of these, represented on the 6-inch map as discharging separately into the Clyde at Southwood, is now a tributary of the other or Wintercleuch Burn [NS 93859 22809]. Not far above the junction of the two streams a small exposure may be seen of pillowy lava associated with the grey cherts. Further up stream the red cherts appear, followed by similar lava and cherts, which are in turn succeeded by a broad mass of coarse ophitic dolerite or gabbro intrusive in the Arenig lava. The relation between the two is displayed on a knob of rock on the north bank of the burn, measuring about eight feet broad and three feet high. Near the head of the stream the volcanic rocks are succeeded by the cherts and black shales repeated by folds.

Wintercleuch Burn. — [NS 93884 22805] For some distance front the railway no rock is visible in this burn, which is nameless on the 1-inch map. About 100 yards above the junction of the two burns the first rock met with consists of coarse dolerite, showing under the microscope much altered felspar and fresh augite. By means of small knobs on the hill slope this coarse-grained intrusive rock can be traced for 400 yards in a south-west direction to the alluvial terraces of the Clyde opposite the foot of Glengonner Water. Higher up the stream the lavas and cherts are repeated by compound folds. Along the strike of these higher folds there is evidence of the development of flaser structure in the lava by mechanical movement. About 170 yards to the W.S.W. of the Wintercleuch Burn, on the north side of a knoll of rock about ten yards broad, near the 1000-feet contour line, the normal diabase-lava is exposed, the pillowy masses measuring in some instances nine inches by seven inches; while the remaining portion shows the same material deformed. In places the nodular masses are flattened, elongated, and surrounded by a schistose matrix; in other parts they disappear, and the rock merges into a green schistose diabase or chlorite-schist. Near the head of the Wintercleuch Burn, the Arenig lava is succeeded by radiolarian cherts, black shales, greywackes, and shales.

Castle Hill, Abington. — [NS 94361 22208] Southwards from Abington along the eastern slope of the Clyde valley, a considerable development of Arenig volcanic rocks and radiolarian cherts may be observed to the north-east of Kirkton. These exposures are interesting, since it is possible to connect the lavas and cherts with the fossiliferous band of black shales seen on the slope near the railway cutting, and hence with the important band in that cutting to be presently described. The accompanying section (Figure 49) is drawn across the brow of the hill in a N.N.W. and S.S.E. direction. At the north-west termination various folds of the cherts (C) and black shales (2I, 3II) appear with greywackes and grits (3). At the old Fort or Camp [NS 95164 21875], marked on the map, the greywackes on the south side of the arch are brought into contact with the cherts, without the black shales intervening. The first appearance of the lava represented in section is about 170 yards to the south of the Camp, while another outcrop, not in the line of section, occurs a little distance to the north of this point. The main exposure, however, is found about 300 yards to the south of the Camp, where it stretches up the hill slope with an average breadth of forty yards, bounded on the north side by the radiolarian cherts. The southern limit is marked by a grassy hollow, which is probably a line of fault, as greywackes immediately succeed. An interesting feature is observable in connection with the volcanic rock; the surface facing the grassy hollow is nodular or brecciated, as if the cooled skin or upper surface had cracked up into pieces which were enveloped in the still molten lava.

Southwards black shales and radiolarian cherts are followed still further south by three small isolated masses of lava, forming inliers in a mass of Arenig cherts. Along the southern margin of these cherts, from a fine exposure of black shales, the following characteristic Glenkiln forms have been collected at a point about 200 yards N.N.E. of the railway cutting [NS 93637 21371] opposite Kirkton:

Caenograptus gracilis (Hall.)

Caenograptus nitidulus (Lapw)

Didymograptus superstes (Lapw)

Dicranograptus formosus (Hopk.)

Dicranograptus minimus (Lapw.)

Dicranograptus ramosus (Hall)

Dicellograptus sextans (Hall.)

Dicellograptus moffatensis (Carr)

Diplograptus foliaceus (March.)

Diplograptus mucronatus (Hall)

Climacograptus bicornis (Hall.)

On the southern slope of Castle Hill eastwards to Southwood Rig [NS 94772 22523], a belt of ground upwards of half a mile in width is composed mainly of plicated Arenig cherts, with black shales forming the outer margins of the folds. The hill slopes are strewn with debris of the radiolarian cherts, and the black shales are visible, sometimes in scars and sometimes in small burns flowing into the Camps Water. Indeed, from the constant repetition of these two zones it is apparent that the strata, though covering so great a breadth of ground, are of no great thickness and have been subjected to much plication. Of the various exposures of black shales the most interesting is to be found in the railway cutting about a mile and a quarter south of Abington.

This section shows the extraordinary disturbed character of these black shale outcrops where they can be studied in detail. The bands are traversed by a series of faults, normal and reversed, which renders an examination of the beds by the zonal method a matter of great difficulty. In the Abington area the strata are frequently so crushed and shattered that fossils are not easily obtained from them.

In the centre of the section, to the south of the railway bridge, a small exposure of the radiolarian cherts is truncated by faults on both sides. North of the bridge the greywackes and shales are brought into contact with the black shales by a fault. The following forms were obtained from this section:

Climacograptus bicornis (Hall.)

Climacograptus peltifer (Lapw.)

Dicellograptus sextans (Hall)

Diplograptus mucronatus (Hall.)

Diplograptus foliaceus (Murch.)

Diplograptus perexcavatus (Lapw)

Cryptograptus tricornis (Carr)

Dicellograptus Forchhammeri (Gein.)

Dicellograptus Forchhammeri var. flexuosus (Lapw)

Dicellograptus intortus (Lapw.)

Dicellograptus elegans (2) (Carr.)

Lasiograptus margaritatus (Lapw)

Lasiogaptus Harknessi (Nich)

Amphigraptus radiatus (Lapw)

Dicranograptus ramosus (Hall)

Corynoides nov. sp.

Acrotreta Nicholsoni (Dav.)

It is clear that graptolites common both to the Glenkiln and the Lower Hartfell zones are met with in this section. Indeed, this assemblage of species proves that some of the bands at least represent the base of the Lower Harden black shales. This supposition is confirmed by the evidence obtained in a quarry at the road-side close to the railway cutting. There the prolongation of the band just referred to is visible, and the section further shows a passage upwards into the greywackes and shales. From one of the thin seams of black shale, which are partly dark sandy shales, in this quarry, excellent specimens of Climacograptus caudatus have been gathered. The palaeontological evidence indicates that the highest zone represented is intermediate between the Pleurograptus linearis zone and the Climacograptus Wilsoni, zone. It is interesting, too, to observe that this evidence is in accordance with that found in the section at the Deil's Barn Door at the head of Wandel Water.

The following is the list of fossils obtained from the quarry beside the railway cutting:

Climacograptus caudatus (Lapw.)

Climacograptus bicornis (Hall.)

Diplograptus mucronatus (Hall.)

Diplograptus perexcavatus (Lapw.)

Glossograptus Hincksi (Hopk)

Corynoides calycularis (Nich)

Acrothele granulata (Linnr.)

When the collection of graptolites was made from the section in the railway cutting, only some of the seams proved fossiliferous; had the band in contact with the radiolarian chert yielded fossils they would probably have belonged to the Glenkiln horizon.

Whelphill Grains. — About two miles to the south-east of Abington, the Clyde receives two tributaries on its right bank, the Camps Water and Midlock Water. Various exposures of black shale are visible at intervals along a line traceable from Whelphill [NS 99321 20525] on the Midlock, by Grains on the Camps Water [NT 00944 22669] (Sheet 16), across the boundary between the counties of Lanark and Peebles, onwards to the sources of the Holms Water above Glencotho [NT 08324 29943]. It is highly probable that some of these may occur on separate inverted folds, and that they may not be prolongations of one and the same continuous outcrop. The black shales occur in grey sandy shales (Lowther Shales) and grits, the beds having a general inclination to the north-west. Several local isoclines of black shale are found near the main folds, as, for example, in the Grains Burn — a tributary of the Camps Water, and the Back Burn south of Culter Waterhead. Owing to the highly contorted and shattered character of most of these black shales, few fossils have been obtained from them. At Whelphill they have supplied Dicellograptus moffatensis much distorted, Diplograptus foliaceus, and Climacograptus; at Grains they have afforded Dicellograptus Forchhammeri, Climacograptus bicornis, and Corynoides calycularis.

In a small tributary of the White Gill, named the Reeve Sike [NT 00066 21763], between Whelphill and the Grains, radiolarian cherts are exposed with the black shales. Again in the Grains Burn, about 440 yards above the Grains shepherd's house, an exposure of black shales on the right bank of the stream furnished the following forms:

Leptograptus flaccidus (Hall)

Diplograptus foliaceus (Murch)

Retiolites (Neurograptus) fibratus (Lapw.)

Glossograptus Hincksi (Hopk.)

Dicellograptus moffatensis (Carr)

Cryptograptus tricornis (Carr)

Climacograptus sp.

Siphbnotreta micula (M'Coy.)

The area between the great complex assemblage of volcanic rocks, radiolarian cherts, and black shales at the head of the Wandel Water and the Whelphill band, about two miles to the south-east, is occupied by a folded series of greywackes and shales with bands of grit and occasionally of conglomerate which have hitherto proved unfossiliferous. In a band of conglomerate in the Back Burn, about half a mile up stream from Culter Waterhead, fragments of chert with radiolaria occur.

The strip of ground between the Whelphill outcrop of black shales and the line marking the base of the Llandovery Rocks in Sheet 16 is occupied by a development of grey and blue shales weathering frequently into a brown or buff colour. Where a fresh fracture can be got they often contain minute specks or spots due to an iron carbonate, the decomposition of which gives rise to the brown tint (Lowther Shales). They are associated with greywackes and pebbly grits, which, however, form a minor feature of the series. Their notable characteristic is the occurrence of nodules of limestone embedded in the shales. Sometimes they coalesce, forming a continuous line of nodules. Occasionally thin ribs of limestone_.:are interleaved in the shales associated with calcareous grits that yield traces of fossils. The limestone nodules can be traced in Sheet 16 of the map for some distance. They appear in a small burn about three-quarters of a mile to the east of Whelphill, and again in a stream on the east slope of Midge bill. Beyond the Camps Water, they can be traced from the head of the Fair Burn to the source of the Whitelaw Burn, on the watershed south of Coomb Dod. They reappear on the north-west of the Singledores Burn, on the slope of the Coomb Hill. At some of these localities, as, for instance, at the head of Fair Burn, Camps Water, the calcareous grit occurs in connection with the nodules of limestone. There can be no doubt that these calcareous nodules and grits represent the well-known Wrae limestone to be described presently. The shales with which they are associated are regarded as the equivalents of the Barren Mudstones of Moffat.

Culter Water district

To the north-east of the complicated area in the upper reaches of the Wandel Water a similar development of Arenig volcanic rocks and overlying sediments may be seen in the various streams that unite to form a tributary of the Culter Water at Birthwood [NT 03046 30907], about two miles south of Culter. Several of these streams rise on the north slope of the watershed in the north-west corner of Sheet 16. On referring to that map it will be seen that a conspicuous arch of diabase-lavas and tuffs, with! the associated radiolarian cherts and black shales, occurs on the watershed, extending eastwards to Duncan Gill and passing into Sheet 24. Attention will be directed first to the sections at the head of these streams connecting the geological structure of the Wandel Basin with that of Culter Water.

Duncan Gill. — From the section in the upper part of Duncan Gill, where its course is north-east and parallel with that of the Birnock Burn, important evidence has been obtained. In a scar on the west bank of the stream, in a line with the gorge of the Deil's Barn Door (ante p. 221) [NT 00818 26554], and separated from it only by a few yards, the radiolarian cherts with the basal red zone are visible at the bottom of the gully. The black shales which then succeed may be traced almost continuously to the Deil's Barn Door section. The graptolites obtained from Duncan Gill include excellent specimens of Climacograptus caudatus, showing that the Lower Hartfell horizon is represented in this part of the Culter Basin.

Further up the stream, the radiolarian cherts are repeated on successive anticlines overlain by the Glenkiln–Hartfell black shales. In the outcrop of black shales in Duncan Gill, 300 yards south of the scar just referred to, Climacograptus caudatus occurs with other graptolites. Nearer the watershed at Duncan Gill Head [NT 00632 25627] this band is succeeded by shales and coarse grits, forming part of the Caradoc formation of this region. The accompanying section (Figure 51) shows the extraordinary folding of the rocks. At the north end of the tract illustrated by this section (Sheet 24 of the Survey Map), greywackes and shales form the high ground, but the Glenkiln–Hartfell Shales come to the surface north of Mere Cleuch, and are repeated by various folds as far as the Eastside Burn. In this stream, at the point where it is joined by the Duncan Gill (on the south margin of Sheet 24), the black shales are seen near the volcanic rocks. Here, on the further side of a fault, a fine exposure of diabase-lava runs for a distance of 150 yards along an isoclinal fold. This inlier of the volcanic rocks is one of the largest in the basin of the Culter Water, since it can be traced for a mile from the Eastside Burn (Sheet 24), south-west by the head of Big Sma'gill, to the watershed at the sources of the Wandel Water (Sheet 16). The main mass is composed of highly amygdaloidal aphanitic diabase (altered basalt), which is much decomposed. The augite is completely altered into chlorite, and the amygdules are filled with calcite. Round the western end of the fold a band of tuff overlies the lava, and is succeeded on the south side by the radiolarian cherts.

The section which continues southwards towards the head of Duncan Gill displays a constant repetition by isoclinal folds of the radiolarian cherts and Glenkiln–Hartfell black shales without exposing the volcanic zone. It is interesting to note, in connection with the wonderful corrugation of the beds in this area, that near the head of Deer Gill — a tributary of Duncan Gill — while the cherts are visible in the bottom of the gorge in continuous section, the outcrop of the overlying black shales can be traced along the top of the west bank repeated by numerous folds (Sheet 16, north-east corner).

Big Sma'gill. — [NT 00439 28713] At the south end of the section in Big Sma'gill that unites with Eastside Burn to form Cow Gill the arch of diabase-lava with overlying (tuff is met with, being the western prolongation of the fold just described at the mouth of Duncan Gill. Owing to a fault, the normal sequence of the cherts is not visible. To the north of the volcanic rocks succeed shales and grits with a bed of conglomerate. A thin band of black shales rapidly appears, followed by shales and pebbly grits. Here for a distance of 100 yards rapidly folded black shales may be observed, which have yielded Climacograptus bicornis, Diplograptus, Corynoides calycularis, and Siphonotreta micula. By a series of isoclinal folds these black shales are repeated with a persistent dip to the N.N.W., and evidently it is chiefly the higher seams that are represented. Northwards, the overlying shales and grits again appear, followed by another fold of the Glenkiln Shales dipping towards the south.

Shank Houp. — [NT 01871 29241] This stream, which runs north to join the Cow Gill about a mile west of Birthwood, on the Culter Water, has a course roughly parallel with that of the Eastside Burn, and exposes a transverse section of the strata. Although it has not laid bare any of the volcanic rocks it reveals the radiolarian cherts on two anticlines, together with the Glenkiln black shales and overlying sediments. Eastwards, along the strike of these folds in the Culter Water, the radiolarian cherts and black shales "nose out", and the anticlines are represented in higher beds, composed of the overlyina grits, greywackes, and shales. Thus as we follow the anticlines from the sources of the Wandel Water to the tributaries of the Culter Water we gradually pass to higher zones. It is reasonable, therefore, to infer that the Caradoc beds are quite as much folded as the underlying Arenig and Llandeilo rocks, though from the absence of recognisable zones it is difficult to prove it.

Woody Cleuch. — [NT 02148 29642] On the north slope of Woodycleuch Dod, a small stream flows into the Shank Houp, which, near the foot, displays the diabase-lava. No rock is visible on the north side of the diabase, but to the south the red nodular cherts immediately succeed, followed by the higher zones and the black shales. By means of isoclinal folds the cherts and Glenkiln black shales reappear, followed towards the south by the greywackes and shales.

We shall now describe a group of sections on the west side of the Culter Water, near the margin of the tableland, and within a mile and a half of the great fault that brings the Old Red Sandstone volcanic rocks into conjunction with the Silurian strata.

Key Gill. — [NT 01149 29960] About a mile and a half to the south-west of Buthwood, on the Culter Water, in a streamlet named the Key Gill; which joins the Cow Gill about 400 yards below the shepherd's house of that name (Figure 52), an excellent exposure of the strata shows their sequence from the radiolarian cherts to an important band of conglomerate, which is regarded as the south-west prolongation of the fossiliferous grit at Kilbucho. This may be regarded as the type-section for this part of the Culter Water basin.

The strata are here arranged in an isoclinal fold dipping towards the S.S.E. In the centre lie the cherts, succeeded immediately by the Glenkiln black shales (2I), followed by grey sandy shales with greywackes (2 & 3). These are overlain in turn by a band of conglomerate and grit (H) representing the horizon of the Kilbucho grit. On the north side of the isocline the outcrop of this bed is a little further distant from the centre of the arch than that on the south side. In its lithological character and modes of weathering this grit closely resembles the fossiliferous grit of Kilbucho to be described in the sequel. It also contains fragments of fossils. A glance at the map will show that the bands of fossiliferous grit on the south slopes of Lamington Hill and Howegill Rig lie much in the same line of strike as the well-known bed at Kilbucho, the various outcrops being due to folds.

On the road between Cow Gill and Lamington House, southwest of Key Gill, an anticline of the radiolarian cherts is locally known as the Giant's Grave. To the west of this exposure, near a small loch, an outcrop of black shales has yielded Climacograptus peltifer, Dicellograptus sextans, D. divaricatus, and Corynoides calycularis.

Howe Gill. — [NT 01470 30654] About half a mile to the east of Key Gill an interesting section is visible in the Howe Gill, which drains the hollow between the Lamington Hill and Howegill Rig (Figure 53). Three successive anticlines expose with great clearness the radiolarian cherts, including both their red and grey sub-zones. In the two northerly folds, and particularly in the central one, the Glenkiln black shales are well displayed immediately overlying the cherts and mudstones. These are succeeded by grey shales and greywackes, with the band of fossiliferous grit which is laid bare in the stream between the central fold and that to the south.

This section is of further interest, because the crest of the hill displays a fine outcrop of the typical "Haggis Rock", pierced by a mass of camptonite. Attention will be directed to the characteristic features of this conglomerate rock as they are developed north of Snaip. Meanwhile it is sufficient to indicate that though the "Haggis Rock" and its associated strata are inclined to the southeast, and apparently dip below the radiolarian cherts and black shales, it seems to occupy the same position relatively to the radiolarian cherts is the representative of the Kilbucho fossiliferous grit. Indeed, the strata generally throughout the Howe Gill dip towards the south-east, and the axes of the various anticlines are therefore inclined in that direction.

The Wind Gill [NT 01952 31051], which joins the Cow Gill about half a mile west of Birthwood, reveals a similar series of isoclinal folds, with the radiolarian cherts in the centre, followed by the Glenkiln black shales, sandy shales, greywackes, and the Kilbucho conglomerate. The underlying volcanic rocks have not been met with in any of these folds in this portion of the Culter Water basin.

Gair Gill. — [NT 02668 32299] In this stream, which flows into the Culter Water about half a mile south of Snaip, an outcrop of black shales has yielded fossils characteristic of the Glenkiln division (Figure 54). The section is not continuous, but in the light of the evidence already adduced it is possible to assign their relative positions to the various groups of strata. At the head of the stream, where it divides into two small "sikes", the Glenkiln black shales dip at a high angle to the south-east, and have there yielded the following forms:

Caenograptus gracilis (Hall.)

Caenograptus pertenuis (Lapw)

Caenograptus surcularis (Hall)

Didymograptus superstes (Lapw.)

Dicranograptus minimus (Lapw.)

Dicranograptus ramosus (Hall.)

Cryptograptus tricornis (Carr.)

Dicellograptus moffatensis (Carr.)

Dicellograptus divaricatus (Hall.)

Dicellograptus patulosus (Lapw.)

Dicellograptus sextans (Hall.)

Diplograptus foliaceus (Murch.)

Diplograptus perexcavatus (Lapw.)

Acrothele granulata (Linnr.)

An analysis of this list shows it to include certain forms exclusively confined to the Glenkiln division, and others which are common to that division and the lower zones of the Lower Hartfell black shales. The assemblage of fossils proves that here the characteristic fauna of the black shale band still overlies the radiolarian cherts as at Abington. In a sike at the head of Gair Gill this black shale apparently comes to the surface along an isoclinal fold, for towards the north it is rapidly succeeded by grey sandy shales, greywackes, and the fossiliferous grit of Kilbucho. Further down the stream, the rocks are buried underneath boulder clay, but soon the radiolarian cherts reappear repeated in folds. They are followed at the bend towards the east by an outcrop of the Glenkiln black shales charged with Dicranograptus zic-zac and other associated forms. On the hill slope towards the Dimple, occasional exposures of green and red mudstones are succeeded by a fine outcrop of the "Haggis Rock" on the top of the Snaip Hill (Figure 54).

Nisbet Burn. — [NT 04194 31912] On the east side of the Culter Water, important evidence is obtained to show the relation of the prolongation of the fossiliferous grit of Kilbucho to the radiolarian cherts and volcanic rocks. In the Nisbet Burn, which joins the Culter Water at Snaip, and also in one of its branches, the Peat Burn, that runs northwards from Tippet Knowe, the lowest visible rocks belong to the volcanic zone. They appear near the foot of the Peat Burn, and consist of diabase-lava, with an outcrop twenty yards in breadth. There they are followed by the radiolarian cherts and by the Glenkiln band of black shales, visible along the line of strike in the Nisbet Burn, where they have yielded traces of graptolites.

The radiolarian cherts come to the surface in two successive anticlines, showing the red and green zones associated with mudstones, one below the junction of Peat Burn and the other at the foot of Hazel Gill [NT 03932 32107]— a rivulet that joins Nisbet Burn from the east, about half a mile south of Nisbet Farmhouse. About two hundred yards to the north of Hazel Gill the Glenkiln black shales are seen in the stream, and still further north the fossiliferous grit of Kilbucho appears on the east bank, about four hundred yards to the south of Nisbet Farmhouse. Here the grit has yielded the following among other fragments of fossils: Leptaena tenuicincta, Orthis sp., and fragments of corals. A reference to the one-inch map (Sheet 24) will show that this outcrop in the Nisbet Burn is quite in the line of strike of the Kilbucho conglomerate to the west of Kilbucho Burn. In the Nisbet Burn, although the strata are isoclinally folded and dip to the south-east at high angles, their order of succession can be established by means of the successive recognisable zones.

The section exposed in the banks of the Culter Water below. Snaip and in the adjoining ridge presents one peculiar feature, viz.: the disappearance of the black shale associated with the radiolarian cherts as it approaches the fault that bounds the Lower Old Red Sandstone at Culter (Figure 55).

At the south-east end of the section, the Glenkiln black shales are visible at the foot of the ridge, on the east bank of the stream, beyond the edge of the alluvium. About 200 yards to the south of their line of strike they reappear on another fold, at the road-side south of Snaip Farmhouse, where they are charged with typical Glenkiln fossils similar to those from the Gair Gill already referred to. To the north of the black shales on the east bank of the Culter Water, the radiolarian cherts succeed, here inverted, and apparently overlying the Glenkiln black shales. They are associated with ashy mudstones, which may possibly indicate a continuance of volcanic activity/ during this stage in the sequence of the zones. Next green shales, mudstones, and greywackes dip steadily towards the north-west. On the top of the ridge (East Mains Hill) a fine exposure of the "Haggis Rock presents the characteristic features of the bed as exposed on the crest of Lamington Hill. It may be described as a fine conglomerate with a greywacke matrix, in which occur abundant fragments of radiolarian chert representing all the zones of that sub-division of the stratigraphical series. As a rule, these materials form by far the largest part of the ingredients. Further, fragments of volcanic rocks may be observed derived from the series underlying the radiolarian zone, also greywacke and mudstone. Rounded grains of quartz are numerous. The rock has frequently a variegated appearance from the different tints of the chert.

A careful search for fossils has been made in the various exposures of the "Haggis Rock", but the results have not been very satisfactory. Fragments of corals, encrinites, brachiopods, &c., have been found, but never in such a state of preservation as to permit of specific identification.

An important development of soft green mudstones, with ribs and bands of sandy greywacke, from six inches to a foot in thickness, is well exposed in a quarry by the road-side about half a mile south of the fault that bounds the Old Red Sandstone. The strata are there inclined to the north, and thrown into a series of isoclinal folds. There can be no doubt that they underlie the "Haggis Rock" on the crest of the East Mains Hill [NT 03316 33682]. The "Haggis Rock" reappears on the hill on the west side of the Culter Water, but is not visible in the stream, which exposes the underlying green mudstones.

The radiolarian cherts are exposed on two anticlines in the Culter Water — one near the Old Red Sandstone fault and the other about 200 yards to the south of that boundary line. They are succeeded directly by the green mudstones without the intervention of the black shales, and dip towards the south-east (Figure 55). This section is not quite so clear as some of those already described, but there can be little doubt that the cherts exposed on the Culter Water near the bounding fault belong to the horizon above the volcanic rocks, though there the graptolite-bearing shales no longer define their horizon. The green mudstones and shales, which seem to be destitute of fossils, occupy a similar position with reference to the radiolarian cherts as the Tappins group in the valley of the Stinchar, above North Balloch.

Biggar Water district

To the north-east of the area described in the foregoing paragraphs a fine development of the volcanic rocks and cherts, passing upwards into the fossiliferous conglomerate and grit of Kilbucho, may be studied in the region of the Biggar Water.

To the south-west of Broughton three well-marked anticlines expose the Arenig volcanic rocks. Of these, the most important are those in the valley of the Kilbucho Burn at Blindewing [NT 07569 34008] and Oakbrae [NT 07551 34583](Figure 56). In a small drain about 100 yards west of Blindewing Farmhouse, the diabase-lava can be seen in a much-altered condition. "The felspar occurs in turbid lath-shaped crystals, penetrating purplish-brown augite. A large portion of the augite is converted into chlorite and serpentinous products. The amygdules are filled with calcite and spherular aggregates of chlorite".

In a quarry, about 500 yards to the south-west of Blindewing, the igneous material has rather the appearance of an intrusive rock. It is there "an ophitic diabase or altered dolerite, composed of turbid plagioclase, augite partly fresh and partly altered, with chlorite, ilmenite, and leucoxene". The flinty mudstones are exposed in the drain near Blindewing Farmhouse on the south side of the diabase-lava; but are concealed on the north side of the fold by a covering of drift.

At Oakbrae, on the north side of the Kilbucho Burn, the south slope of the Goseland Hill supplies another exposure of the diabase-lava in a quarry at the road-side about 400 yards south of Goseland Farmhouse. Here the slaggy character of the rock is well displayed. The lava is bounded on both sides by the radiolarian cherts. On the crest of the anticline at a distance of 300 yards, the volcanic rocks "nose out" and disappear under the cherts, but they come to the surface again about 700 yards to the east, in the form of lava of a more acid character, displaying a ropy surface which has not been denuded. Throughout the felsitic matrix are scattered porphyritic crystals of plagioclase felspar. This rock is traversed by a series of fissures now filled with chert — a feature which seems to point to the conclusion that the igneous material was erupted contemporaneously with the strata among which it lies.

On the north limb of the arch of the volcanic zone at Oakbrae, the radiolarian cherts are repeated by numerous folds, till within a short distance of Goseland Farmhouse the Glenkiln band of black shales succeeds to them, followed in turn by shales and greywackes. On the south limb the black flinty shales also occur on the south side of the cherts, so that in the Kilbucho area the normal succession of deposits overlies the volcanic zone.

About a mile further to the west the Kilbucho conglomerate and associated strata lie in the centre of a series of folds, with the volcanic rocks and cherts underneath. On the Manse Rig [NT 06185 33193] the prolongation of the fold with the volcanic rocks at Blindewing, just described, is represented in the radiolarian cherts. Not far to the south the diabase-lavas occur on another fold.

In the burn above the old manse of Kilbucho the rocks are obscured by drift, but on the north side of the stream the fossiliferous conglomerate of Kilbucho is exposed in a quarry about half a mile to the west of the old manse. In lithological character and mode of occurrence it resembles the fossiliferous band at Wallace's Cast, Wandel Water. It has a greywacke matrix, grey in fresh fracture, containing large shale galls or shaly lenticles that give the rock a banded appearance. Further it passes laterally into shales. Limestone nodules occur both in the conglomerate and in the shales. Owing to the decomposition of its carbonates, the rock weathers a rusty brown; the limestone nodules decompose and crumble away into a brown earth. Among the pebbles, the prominent constituent is white vein-quartz in small well-rounded pieces; fragments of radiolarian chert also occur, but in a lesser degree than in the typical "Haggis Rock", and occasionally the Arenig volcanic rocks are represented by minute particles. The fossils occur here in the same way as they do at Wallace's Cast and at Duntercleuch, Leadhills. A comparison of the accompanying list of fossils obtained from the quarry at Kilbucho leaves little room for doubt that the assemblage is identical with that from Wallace's Cast, thus proving the Caradoc age of the beds:

Nidulites favus (Salter.)

Glyptocrinus basalis (M'Coy.)

Encrinite stems.

Stenopora (Favosites) fibrosa (Gold.)

Petraia bina (Lonsd.)

Petraia uniserialis (M'Coy.)

Lindströmia (Petraia) subduplicata (M'Coy)

Lindströmia (Petraia) var. crenulata (M'Coy.)

Ptitodictya costellata (M'Coy.)

Leptaena scissa (Salt.)

Leptaena sericea (Sow.)

Leptaena (Christiania) tenuicincta (M'Coy.)

Leptaena (Plectambonites) transversalis (Wahl.)

Orthis crispa (M'Coy.)

Orthis calligramma (Dalm.)

Orthis protensa (Sow.)

Orthis rustica (Sow.)

Orthis unguis (Sow.)

Strophomena kilbuchoensis (Dav.)

Strophomena (Leptaena) rhomboidalis (Wick.)

Modiolopsis orbicularis (Sow.)

Ecculiomphalus sp.

Murchisonia angulata (Sow.)

Platyschisma helicites (Sow.)

Pleurotomaria (Raphistoma) elliptica (His.)

Pleurotomaria (Raphistoma) lenticularis (Sow.)

Orthoceras sp.

Cheirurus clavifrons (Dalm.)

Phacops alifrons (Salt.)

Phacops Brongniarti (Portl.)

Trinucleus sp. (punctate fringe.)

The fossiliferous grits and shales occupy the hill to the north of the quarry, but the radiolarian zone reappears in several folds on the Hartree Hills [NT 06159 35901] (Figure 57). An excellent section may be seen by the road-side crossing the hill in a north-west direction from Goseland Farmhouse, but though the exposures are more or less continuous, the black shales have not been detected there. The cherts seem to pass upwards into red and green mudstones, followed by shales, grits, and the "Haggis Rock" conglomerate.

In the area east of Biggar Water, the first exposure of the volcanic zone is found on the Pisgah Hill [NT 07708 37450], about two and a half miles west of Broughton (Figure 58). In the centre of the fold the slaggy diabase-lava (1 B) is met with, overlain on the south side by the red cherts and mudstones (C). In a field to the west of a narrow belt of wood, from an isolated exposure of black shales (2I), a small but interesting assemblage of fossils has been obtained, viz.: Diplograptus foliaceus, Climacograptus bicornis, Dicellograptus moffatensis, and Siphonotreta micula. This list shows that even here certain forms common both to the Glenkiln and Hartfell divisions occur together. And yet the strike of this fold on Pisgah Hill seems to lie rather to the north of the strike of the anticlines in the Culter Water north of Snaip, near the fault bounding the Old Red Sandstone, where the black shales seem to have disappeared. Further evidence of this spasmodic occurrence of the Glenkiln black shales to the north-east of Pisgah Hill will be adduced.

On the north side of the volcanic rocks a fault bringing down the overlying pebbly grits, resembling the fine-grained "Haggis Rock", probably occurs. There is no evidence on that limb of the fold of the existence of the cherts and mudstones. It must be remembered that the rock exposures on this hill are not continuous, and that the diagram has been constructed from isolated exposures.

A remarkable series of outcrops of the radiolarian zone occurs on the ridge that extends from Broughton [NT 11214 36716] N.N.W. to Broughton Knowe [NT 09466 39343] — a distance of about two miles — which shows the extraordinary reduplication of the strata by means of isoclinal folds (Figure 59). The dip is towards the south-east, as if there were an ascending series in that direction; but by means of the different stratigraphical zones it is possible to prove that the actual thickness of strata represented in this section cannot exceed a few hundred feet.

There are here twelve anticlines which bring up either the radiolarian cherts as the lowest zone or sometimes even the underlying volcanic rocks. Of these folds, the two most important occur at Broughton Knowe, where, within half a mile of the fault bounding the Old Red Sandstone, they expose the volcanic rocks in the core of the arch. In the most northerly fold the igneous materials, consisting mainly of amygdaloidal diabase-lavas, can be traced for a mile and a half along the strike. About 200 yards north-east of the farmhouse of Broughton Knowe, at the road-side, coarse volcanic agglomerates occur. To these volcanic ejectamenta succeed the cherts, with red and green mudstones. Round Skirling Craigs, however, the mudstones seem to have in great measure replaced the cherts. About 100 yards to the north-east of the farmhouse of Broughton Knowe debris of black shales is visible on the surface. The volcanic rocks reappear on a second fold about 150 yards to the south of the main arch at Broughton Knowe.

For nearly a mile along the top of the ridge from Broughton Knowe to a point about three-quarters of a mile from Broughton village, there is a constant repetition of the cherts and mudstones, with dark flinty and grey sandy shales. At the edge of the Drove Road, about a mile W.N.W. of Broughton, the black shales have yielded Cryptograptus tricornis, Dicranograptus ramosus, Climacograptus, and Dicellograptus. To the north, the radiolarian cherts and black shales pass underneath grey sandy shales and greywackes containing Diplograptus foliaceus. A similar occurrence has been noted in the case of the grey sandy shales in Hawkwood Burn, opposite Birnock, which overlie the outcrop of Glenkiln black shales (p. 219). The remaining portion of the section near Broughton is constructed from evidence seen partly in the Drove Road, in quarries, and in the stream near the village.

In the area that borders the Old Red Sandstone between the Broughton [NT 11214 36716] and Tarth Burns [NT 12320 47278], similar evidence is obtained of the remarkable reduplication of the strata. Throughout this tract (shown in section in (Figure 60)), the strata have a persistent dip to the south-east at high angles. Near the fault bounding the Old Red Sandstone, the diabase-lavas are exposed on several sharp anticlines, followed by the cherts and mudstones, without the intercalation of any black shales above the cherts. Indeed, the black shales have not been detected in the various folds near the Old Red Sandstone rocks between Broughton Burn and Tarth Water. At one locality, about a third of a mile S.S.W. of Old Harestanes [NT 12320 44096], fragments of chert occur in a matrix resembling mudstone, in association with the volcanic rocks. About three-quarters of a mile S.S.E. of Old Harestanes, from an isolated exposure of black shales, Diplograptus has been collected.

On the Lochurd Hill [NT 12504 42238], Wether Law [NT 12646 41495], and Pyked Stane Hill [NT 12286 41094], north of Broughton Heights, black shales accompany the cherts. At one locality a graptolite was obtained which resembled Climacograptus caelatus (Lapw.). Though the volcanic rocks are not here visible in the line of section, the diabase-lavas occur in mass on the col north of Flint Hill, about a mile to the east, as will be presently shown. Towards the south, the Arenig rocks and black shales pass underneath greywackes and shales.

District stretching from the Basins of the Tarth and Lyne Waters to the Midlothian Coal-field.

Flint Hill to Woolshears Hill, Castlecraig. — [NT 13786 40718], [NT 13854 42419] A. section roughly parallel with that just described extends from the Flint Hill (over 1500 feet) northwards to the Woolshears Hill (1317 feet), south of Castlecraig policies [NT 13659 44176] , and overlooking the valley of the Tarth Water. Along this ridge for a distance of about a mile, similar evidence is obtained of the constant repetition by isoclinal folds of the Arenig radiolarian cherts, black shales, and other sediments, with a prevailing dip to the S.S.E. The cherts are visible on eleven separate folds, the best exposure being on the north and north-west face of the Brown Dod [NT 13468 41317] (1795 feet), about a quarter of a mile north of Flint Hill, where crags are formed by the cherts which dip S.S.E. at 70°. On the upper surfaces of these cherts the mammilated character of some of the bands is very conspicuous. The grey cherts are in excellent preservation, and in some cases are stained so as to be suitable for microscopic examination of the contained radiolaria. They are also traversed by quartz veins.

An important feature in this section is a fine exposure of Arenig lava in the Ramsgill Crag [NT 13739 41141] on the col between the Flint Hill and the Brown Dod. Here a prominent crag, about 50 yards long and 20 feet high, shows the characteristic pillowy structure so typical of the lavas of Ballantrae. The rock is remarkably fresh, vesicular in places, and resembles the fine-grained diabase type. This oval-shaped mass of lava is bounded by bright green turf, and its relations to the surrounding rocks are not visible. But within a few yards from it the cherts appear to the south-west and northwest. A short distance from its south-western termination a very small exposure of black shales occurs on both sides of the cherts, yielding Dicranograptus minimus, Diplograptus foliaceus, Cryptograptus tricornis, and Climacograptus. These strata are followed on each side by grits and shales.

Tarth Water. — [NT 14123 44704] Advancing now further to the north-east we find in the area that borders the bounding fault between the Tarth and Lyne Waters evidence of the local occurrence of a thin seam of black shale between the volcanic rocks and radiolarian cherts. The igneous materials, consisting of amygdaloidal diabase-lavas, are visible on two anticlines in this district. The more southerly exposure of the volcanic zone is traceable for nearly a mile from the alluvium at Scotston to near Callands Head. Between Scotston and the alluvial flat of the Lyne the breadth of the arch of volcanic rocks is about 200 yards, but at Scotston House it narrows to less than a third of this extent. A few yards to the south of Scotston House [NT 14240 45296]the diabase-lava is succeeded northwards by the radiolarian cherts and red and green mudstones; but the strata are inverted and dip towards the southeast. The mudstones are followed northwards by grits and shales exposed to the east of Scotston House. About a quarter of a mile to the east of Scotston House the diabase comes to the surface along two isoclinal folds, succeeded by the cherts with red and green mudstones. About half a mile north-east of Scotston, pebbly greywackes, with red and green mudstones, probably represent the horizon of the "Haggis Rock". In the area between the Tarth and Lyne Waters, the red and green mudstones are remarkably developed, and show intermediate stages towards the pure radiolarian chart. No black shales have here been observed overlying the cherts.

Tract between the Lyne Water and Lamancha. — From the Lyne Water [NT 16390 44734]  north-eastwards to Riddenlees [NT 20479 51058], south of Lamancha Station, a distance of four miles — within a belt of ground about a mile in breadth, bordering the Old Red Sandstone and Carboniferous strata — the Arenig volcanic zone comes to the surface along numerous anticlines. In most cases the volcanic rocks are traceable for no great distance — sometimes only for a quarter of a mile, sometimes for a mile. In some of these exposures the slaggy character of the diabase-lava is remarkably apparent. For example, in a quarry on the south-east side of the road from Noblehouse to Grassfield, and about three-quarters of a mile from the former locality, there is an excellent exposure of the lava. Here the rock is very amygdaloidal, and the vesicles are filled with calcite, which decomposes on weathered surfaces. So abundant are these amygdules that the rock resembles a lava of younger Palaeozoic age. In all the exposures where a sequence is visible, the diabase-lavas are invariably associated with radiolarian cherts and mudstones passing upwards into red and green mudstones, shales, and greywackes, while in several exposures the black shales are visible, charged with typical Glenkiln forms. In this belt of ground also, as in the region bordering the Old Red Sandstone fault already described, the strata have a persistent dip to the south-east, and hence the folds are isoclinal.

The accompanying section (Figure 61) shows the relations of the strata in the tract bordering the Midlothian coal-field, about a mile south of Lamancha. It is drawn from a point near Whitemuir [NT 19159 51107]  in the Carboniferous area, south-eastwards in the direction of Grassfield. Beginning at the great fault and advancing southeastwards, the sequence of strata is visible in a small burn flowing towards Whitemuir Farmhouse. Near the fault green shales and mudstones are met with, followed by a pebbly conglomerate representing the "Haggis Rock", which here probably occupies a synclinal fold. Southwards the shales and mudstones reappear, succeeded by the radiolarian cherts and mudstones underlain by a small exposure of diabase-lava.

About 400 yards from the fault, a second fold reveals the volcanic rocks, which are traceable along the strike for nearly a mile. On the south side of this arch the red mudstones and cherts follow in natural order, succeeded by the grey mudstones, when a gap occurs in the section, no rocks being visible until, a short distance to the east, the volcanic rocks appear on a third fold, which is of special interest from the occurrence of a black shale band with Glenkiln graptolites, seen in a small burn about 400 yards S.S.W. of Riddenlees [NT 20198 50640], and about 700 yards north of Grassfield [NT 20474 50684]. Here the lava exposed on the north side of the burn is overlain by the cherts and mudstones.

On the same side of the stream a thin seam of blue-black shale, ten to twelve feet thick, occurs apparently in the middle of the cherts, and probably in a synclinal fold. From this seam the following interesting assemblage of fossils has been collected:

Didymograptus superstes (Lapw.)

Caenograptus gracilis (Hall.)

Caenograptus pertenuis (Lapw.)

Caenograptus surcularis (Hall.)

Dicranograptus minimus (Lapw.)

Dicranograptus formosus (Hopk.)

Dicranograptus ramosus (Hall.)

Diplograptus euglyphus (Lapw.)

Diplograptus foliaceus (Murch.)

Diplograptus perexcavatus (Lapw.)

Cryptograptus tricornis (Carr.)

Climacograptus Schärenbergi (Lapw.)

Dicellograptus patulosus (Lapw.)

Dicellograptus sextans (Hall.)

Dicellograptus divaricatus (Hall.)

Acrothele granulata (Linnr.)

Brachiopod.

An analysis of this list shows that while it contains certain forms that are confined exclusively to the Glenkiln division, it includes also some which pass upwards into the base of the Lower Hartfell black shales.

Further east another interesting exposure of the diabase-lava may be seen in the burn near the Riddenlees Farmhouse [NT 20483 51124]. On the north side of the house, by the side of the road leading back to the burn, the black shales are visible in a shattered condition, and apparently in contact with the lava. Here they are probably faulted against the volcanic rocks.

From the evidence now adduced, it is manifest that along the belt of ground extending from Abington by Culter Water and Broughton to where the Silurian rocks come against the Carboniferous formations of the Midlothian basin, the Arenig volcanic rocks, radiolarian cherts, Glenkiln black shales, and overlying sediments are admirably developed and have been laid open on numerous anticlines, which are almost always inverted. By means of the zonal method of interpreting the sections, the extraordinary reduplication of the strata is well shown.

There is one feature, however, to which special attention must be directed, viz., that the axes of the various folds of the Silurian strata between the Broughton Burn and Leadburn, east of Lamancha, are more easterly than the course of the great fault that brings the Carboniferous and Old Red Sandstone strata into conjunction with the Silurian rocks. Hence it follows that the Silurian anticlines are truncated in succession by the great fault, so that as we advance towards the north-east we pass fold after fold of the volcanic series, each in turn being further removed from the Central Moffat region.

Having described the various folds of Arenig lavas and cherts traceable along the margin of the tableland from the Lyne Water to Leadburn, we will now proceed to indicate the occurrence of these rocks with the black shales further south along a parallel belt of ground, three miles in width, between the Lyne Water and Eddleston Station.

Fingland Burn. — [NT 34121 32599] The Flemington Burn [NT 16523 45149], which joins the Lyne Water from the east about two miles to the south of Romanno Bridge, receives a tributary named the Fingland Burn, that drains part of the hilly ground north of the Cloich Hills. About a mile and a half up the Fingland Burn a small outcrop of flinty black shales appears, from which the following characteristic assemblage of Glenkiln graptolites has been collected:

Didymograptus superstes (Lapw.)

Didymograptus serratulus (Hall.)

Climacograptus caelatus var. antiquus (Lapw.)

Climacograptus Schärenbergi (Lapw.)

Climacograptus sp.

Diplograptus euglyphus (Lapw.)

Diplograptus foliaceus (Murch.)

Diplograptus perexcanatus (Lapw.)

Cryptograptus tricornis (Carr.)

Dicranograptus ramosus (Hall.)

Dicellograptus sextans (Hall.)

Caenograptus gracilis (Hall.)

Towards the W.S.W. the debris of this band can be traced in drains for a quarter of a mile, while towards the E.N.E. the strata are buried under boulder clay for a short distance, till on the col at the head of the burn the black shales reappear, but in so crushed a condition that no fossils have been obtained from them. In the Flemington Burn the black shales are succeeded on both sides by olive-green mudstones and thin greywacke bands, resembling the beds on the Tappins Hill in the valley of the Stinchar, Ayrshire. About 200 yards to the north of this black shale band the radiolarian cherts are met with in quarries, much in the same line of strike as the arches of Arenig lavas south of Romanno Mains, previously described. About half a mile to the south of the same band, two folds of radiolarian cherts and black shales are visible in the Fingland Burn at a short distance from each other. The strata in the northern arch are much shattered, black flinty shales being associated with the cherts. They can be traced towards the north-east for a distance of a mile and a half, as far as the slopes of the Wether Law, where, owing to the pitch of the folds, they disappear under greywackes and shales. The southern arch reveals the cherts without the black shales, the strata visible between the two arches being composed of grits and green shales.

On the west side of the Fingland valley, the cherts and black shales are exposed in three arches on Drum Maw Hill [NT 17665 47079], in the strike of the folds just referred to. Half a mile to the southwest of Drum Maw Hill, the black shale reappears in a small exposure, and has furnished the following fossils:

Diplograptus euglyphus (Lapw.)

Diplograptus foliaceus (Murch.)

Climacograptus Schärenbergi (Lapw.)

Climacograptus bicornis (Hall.)

Cryptograptus tricornis (Carr.)

Dicellograptus Forchhammeri (Gein.)

Dicellograptus moffatensis (Carr.)

Dicellograptus sextans (Hall.)

Dicellograptus patulosus var. B. (Lapw.)

Siphonotreta micula (M'Coy.)

In connection with this series of compound folds of the radiolarian cherts and black shales, reference may be made to the occurrence of a band of coarse grit on the slope half a mile S.S.W. of Wether Law, above the cultivated ground at Fingland. It resembles a coarse "Haggis Rock" or pebbly grit, and contains, in addition to the usual fragments of radiolarian chert and volcanic rocks, numerous nodules of blue limestone, varying in size from mere grains to masses two feet in diameter and resembling the conglomerates of Duntercleuch, Kilbucho, and Wrae.

Eddleston and Drochil Castle. — [NT 24277 47117], [NT 16206 43405] About a mile to the south of the folds of the Moffat series described in the foregoing paragraphs, several compound arches of radiolarian cherts and black shales can be followed at intervals from Eddleston south-westwards to Drochil Castle on the Lyne Water. Some of these exposures of black shales yield a definite assemblage of Hartfell fossils. For example, in the glen at Darn Hall [NT 23621 47270], less than half a mile west of Eddleston Station, on the Peebles branch of the North British Railway, blue-black strains appear in grey shales, which, from the following assemblage of organic remains, evidently represent part of the lower Hartfell black shales:

Diplograptus foliaceus (Murch.)

Climacograptus candatus (Lapw.)

Climacograptus bicornis (Hall.)

Lasiograptus margaritatus (Lapw.)

Dicellograptus Forchhammeri (Gein.)

Dicranograptus ramosus (Hall.)

Acrotreta Nicholsoni (Dav.)

Siphonotreta micula (M'Coy.)

Acrothele or Obolella.

These shales are interbedded with greywackes and shales, the whole series dipping towards the south-east.

Advancing westwards, about a mile and a half west of Eddleston and to the north of the forking of the Fairydean Burn [NT 23096 47367], the observer finds an exposure of radiolarian cherts, which he can also follow along the northern slope and on the crest of Kilrubie Hill [NT 21425 46912], on several anticlines separated by greywackes. On the north-east side of the same hill, black shales are associated with the cherts. By means of debris and rock exposures one of these folds of Arenig cherts can be traced south-westwards along the ridge from Kilrubie Hill to the head of Harehope Burn and Crailzie Hill. Still further to the west, on Wide Hope Shank Hill, about half a mile south-west of Crailzie Hill, a series of compound folds of the cherts sometimes reveals the black shales. One fold on the northern slope lies close to the outcrop of a band of "Haggis Rock" or pebbly grit; another fold on the southern declivity displays pillowy diabase-lava which, along the north margin of the exposure, appears to be faulted against greywackes. On the further side of a small stream half a mile north-east of Stevenson Hill the diabase-lava may be seen in association with radiolarian chert on the north side of the arch. Here there is a considerable exposure of decomposing vesicular igneous rock, and its outcrop westwards can be traced on the White Rig by the brighter green of the vegetation, indicating the more fertile soil to which this decomposition gives rise.

The radiolarian cherts that appear on the separate folds just described seem to coalesce so as to form a broad compound anticline on the crest of the hill, a mile E.N.E. of Drochil Castle; indeed, the debris of chert is conspicuous on the coomb-like hollow at the head of the valley formed by the burn east of Stevenson Hill. This zone is hidden under the drift which fills that valley, but reappears on the southern slope of the Wood Hill [NT 16587 43870], above the Lyne Water. On this hill, about 100 yards to the north of its summit [NT 16988 44555], an outcrop of decomposing basic lava occurs among debris of cherts and black shales, the radiolarian cherts being traceable westwards to the level of the 900-feet contour line and for some distance eastwards; while a second exposure of the diabase-lava in the hollow [NT 17869 44758] between Wood Hill and Wide Hope Shank Hill lies rather to the south of the strike of the fold just alluded to. Again, on the north slope of the wood, at the upper limit of the cultivated ground, another exposure of the volcanic rocks is indicated by their abundant debris, together with fragments of cherts and black shales.

On the Drochil Hills [NT 15524 44124], forming the ridge between the Tarth and Lyne Waters, no fewer than eight anticlines may be observed within a distance of half a mile across the strike, some displaying black shales only, others black shales and radiolarian cherts, while a fourth fold, a few yards to the west of the crest of the ridge, reveals the slaggy pillowy lava.

Eddleston Water, North of Eddleston. — In the district of Eddleston Water, north of Eddleston Station, a few sections show the radiolarian cherts and black shales, one of which (Cowie's Linn. Burn) is important, as it furnishes a characteristic assemblage of Glenkiln graptolites in sandy black shales streaked with grey shales.

Cowie's Linn Burn. — [NT 23902 51194] This stream, which unites with the Eddleston Water about 2½ miles north of Eddleston Station, traverses the cherts, black shales with Glenkiln fossils, and overlying sediments. About a quarter of a mile up stream from the railway bridge, greywackes and shales appear, in a crushed condition and dipping in different directions. At a prominent bend in the burn, a few hundred yards further up [NT 23715 51249], several exposures of crushed sandy black shales streaked with grey shales appear, probably on the crests of several anticlines. On the north bank a small part of these shales, not quite so much shattered as the remaining portions, has yielded the following assemblage of Glenkiln graptolites:

Lasiograptus bimucronatus (Nich.)

Climacograptus bicornis (Hall.)

Climacograptus caelatus var. antiquus (Lapw.)

Climacograptus Schärenbergi (Lapw.)

Diplograptus foliaceus (Murch.)

Diplograptus euglyphus (Lapw.)

Caenograptus gracilis (Hall.)

Caenograptus pertenuis (Lapw.)

Dicranograptus ramosus (Hall.)

Dicranograptus formosus (Hopk.)

Dicellograptus sextans (Hall.)

Cryptograptus tricornis (Carr.)

A small arch of radiolarian cherts a few feet in length may here-be traced across the stream. Near these cherts, and in the bed of the burn, the following graptolites were collected from black sandy micaceous shales with grey shales:

Didymograptus superstes (Lapw.)

Caenograptus pertenuis (Lapw.)

Climacograptus caelatus var. antiquus (Lapw.)

Lasiograptus bimucronatus (Nich.)

Cryptograptus tricornis (Carr.)

Dicranograptus ramosus (Hall.)

In the high scar on the north bank, just above where some shattered black shales are pierced by intrusive igneous material, a seam of black shales contains Climacograptus and Dicellograptus. On the opposite bank, in the cliff bounding the south side of the gorge above the prominent bend, the radiolarian cherts appear in force and form the greater part of the precipice. Further up, greywackes and shales are met with which are thrown into a series of anticlines and synclines, well seen at Cowie's Linn. To the north of the Linn, grey shales, visible on the banks, at the edge of the alluvium of the burn, lithologically resemble the Upper Silurian green and grey shaly mudstones of the Pentlands, Lesmahagow, and Kirkcudbright, and yet from certain rusty-weathering bands characteristic Glenkiln forms were obtained, viz.: Didymograptus superstes, Diplograptus euglyphus, D. foliaceus, and Climacograptus bicornis. It appears, therefore, that the horizon of the Glenkiln shales is here represented by ordinary sediment.

Portmore. — About a mile and a half north of Eddleston Station, at the Gala Bank, the radiolarian cherts are displayed in perhaps the finest exposure in the north-west part of Sheet 24 of the Survey Map. About 250 yards east of the Edinburgh and Peebles Road, in a field north of the policies surrounding Portmore House [NT 25050 48835], the cherts appear at intervals for a distance of 200 yards across the strike. They display the red, grey, and green nodular varieties, with radiolaria in abundance. They are best seen on the south side of a small gully, where they form a rocky cliff, being brought into conjunction with the grey shales on the north side by a fault, with a downthrow to the north. A band of black shales appears on the south bank of the gully, and is there associated with the cherts; it can be followed up the cliff, gradually widening out, until at the top it may be seen lying in a fold of the cherts. From this locality the following forms were obtained: Diplograptus euglyphus, Corynoides calyculcuris, C. nov. sp., and Diplograptus foliaceus.

The north side of the gully is occupied by grey shales and greywackes, which dip south-easterly at 70°, and are traceable eastwards as far as the spring, where they are covered with drift. About 700 yards to the north-east, the cherts reappear in knolls in a field and in a road round the edge of a wood west of Portmore Loch. They are also seen in the wood. On the east margin of Portmore Loch [NT 26325 50147], greywackes and shales rise in the line of strike of the folds of chert to the west. The strata in this region generally dip to the south-east.