Figures and plates

Figures

(Figure 1) Two-foot ellipsoids. Chapel, 500 yards north of Llanfwrog Church.

(Figure 2) Pebbles of old schist in Skerries Grits, Bwlch. Natural size

(Figure 3) Deformed boulder. 8 inches long. The Skerries.

(Figure 4) Peacoids of grit in Gwna Mélange. North of Glyn-afon.

(Figure 5) Peacoids of grit in Gwna Mélange. North of Glyn-afon.

(Figure 6) Venous-quartz phacoids, Aethwy region.

(Figure 7) Broken zircon in Bodafon quartzite. Highly magnified.

(Figure 8) Compound oolitic grain in Gwna Limestone. (E10816) [SH 375 946]

(Figure 9).Old foliation in Coedana granite West-south-wst of Coedana Church.

(Figure 10) The felsitic survival. Scale 1:5,000. F=Felsite, M=Mica-schist, Mhb=Hornblende-schist

(Figure 11) Position of passage in Mynydd Llwydiarth. From the six-inch map. Dashes and dots=Gwna Green-schist. Dashes=Penmynydd Mica-schist. Crosses=Basic rocks. Dykes also shown.

(Figure 12) Hornblende-gneiss in granular albite. North boss on east margin of Werthyr alluvium. ×1/2

(Figure 13) Six-inch knot of albite-pegmatite in hornblende-gneiss. 200 yards north-north-west of Craig-yr-allor.

(Figure 14) Six-inch and four-foot sills of albite-pegmatite in hornblende-gneiss. West and north-west of Clegir-mawr.

(Figure 15) Six-inch and four-foot sills of albite-pegmatite in hornblende-gneiss. West and north-west of Clegir-mawr.

(Figure 16) Coarse albite-pegmatite isolating hornblende-gneiss. Height: 1 ft. 6 in. High boss, 200 yards north-west of road-fork at Clegir-mawr.

(Figure 17) Coarse albite-pegmatite isolating hornblende-gneiss. Height: 2 ft. High boss, 200 yards north-west of road-fork at Clegir-mawr.

(Figure 18) Coarse albite-pegmatite isolating hornblende-gneiss. Height: 1 ft. 6 in. High boss, 200 yards north-west of road-fork at Clegir-mawr.

(Figure 19) Inclusions (up to two feet in length) of gneiss in albite-granite. About 330 yards east-north-east of Llandrygarn Church.

(Figure 20) Inclusions (up to two feet in length) of gneiss in albite-granite. About 330 yards east-north-east of Llandrygarn Church.

(Figure 21) One-foot granitoid band cutting thin granitoid bands North-east of Henblâs.

(Figure 22) Granites in gneiss. Coast of the Gader Inlier. Height, about three feet.

(Figure 23) Granite in gneiss. Coast of the Gader Inlier. Height, about two feet.

(Figure 24) Gneiss with lenticular albite-granites. Gwyndy crags. Height, two feet.

(Figure 25) Passage of gneiss into albite-granite. Gwyndy Crags.

(Figure 26) films of gneiss in granite. Coast of the gader inlier. Plan 18 inches long.

(Figure 27) Rejuvenated albites. 1, 2, 3, 4 from (E10151) [SH 241 829] 5, 6 from (E10131) [SH 217 805].

(Figure 28) Infolded outlier of Holyhead Quartzite on the South Stack Moor. At the 500 foot contour. Height of section, 60 feet.

(Figure 29) Spilitic Tuff and Passage Beds. Crag at small farm (Cae-allt-wen) north of 'H' of 'Holy.' Scale, 24 inches = one mile. SSS = South Stack Series. ST = Spilitic Tuff.

(Figure 30) Spilitic Tuff and Passage Beds, Bodwradd. 500 yards north of west of Bodwradd. (LIwyn Beds taken in on pitch immediately to north-east.) Height, about 20 feet.

(Figure 31) Spilitic Tuff (ST), Passage Beds, and South Stack Series (SSS), At Lifeboat Cove, Rhoscolyn. Height, about 30 feet.

(Figure 32) Passage from Fydlyn to Gwna Beds. About 10 feet high. Brow of Fydlyn Cliff.

(Figure 33) The North Stack Fault, Seen from the Signal Station. Height, 400–500 feet. HQ = Holyhead Quartzite. SSS=South Stark Series.

(Figure 34) The Namarch Fault at Porth Namarch. Height about 50–60 feet. South Stack Series to the right: Quartaite to the left.

(Figure 35) Diagram of the recumbent folds of the Mona Complex.All thrusts omitted.

(Figure 36) Major isoclines in Llwyn Beds In the chasm of the dyke. North cliffs of Henborth. Height, about 200 feet.

(Figure 37) Folds of the Llwyn Beds At one-eighth of a mile west of Porth Dafarch. Height, 80 feet.

(Figure 38) Foliation in massive and fissile beds. Cliff opposite the South Stack.

(Figure 39) Minor isoclines with overdrive opposite to that of major fold. Rhoscolyn Mountain (208-foot hill) (a) height of cliff, about 100 feet, junction of quartzite and south stack series. (b) detail, enlarged. (c) similar structures at the fissile seam in the quartzite.

(Figure 40) Folding in Amlwch Beds. Moor, top of Ednyfed Hill, Amlwch Port. Height, two feet. Isoclines becoming locally symmetrical.

(Figure 41) Section between tunnels, Bodorgan. About 30 feet deep.

(Figure 42) Minor folding on vertical axes in the Middle Region. Gwna Green-schist, 500 yards south-east by south from Pen-y-graig, of 600 yards north by east from Bryn-yr-odyn.

(Figure 43) Minor folding on vertical axes in tile Middle Region. Gwna Green-schist, 500 yards south-east by south from Pen-y-graig, of 600 yards north by east from Bryn-yr-odyn.

(Figure 44) Minor isoclines in Soldier's Point Beds, Tipper Road Cutting, Government House. Three and four inches in amplitude.

(Figure 45) Minor isoclines in Celyn Beds. Breakwater Cove. Amplitude three inches.

(Figure 46) Minor isoclines and thrust in Celyn Beds. Breakwater bosses. Length four inches.

(Figure 47) Minor isoclines in Celyn Beds Mynydd Celyn. Height about one foot.

(Figure 48) Minor isocline of a few feet amplitude. in Clwyn Beds. North-west of Gors-goch.

(Figure 49) Folding in Amlwch Beds. Half-a-mile west of Bryn-eilian. Height about two feet.

(Figure 50) Minor isoclines of two feet amplitude in hornblende-schist. 566 yards north-west of Bryn-eryr, Aethwy Region.

(Figure 51) Sharp two-foot isocline in hornblende-schist. Gigfran, Mynydd Llwydiarth.

(Figure 52) Straight-limbed isoclines. Western Cliffs of Point Lynas. (a), (b) Limbs 30 to 40 feet in length. (c) Limbs three feet in length.

(Figure 53) Flat-limbed isoclines. South of Porth-y-felin, Holyhead.

(Figure 54) A-clinal minor folding. (a) Diagrammatic. (b) Drawn from Nature. West side of slack, north-west of Ty'n-y-rnynydd-east, Mynydd Llwydiarth.

(Figure 55) A-clinal minor folding. A little north of Ty'n-y mynydd-east, Mynydd Llwydiarth.

(Figure 56) A-clinal folding of hornblende-schist in mica-schist. West shore of Elusendai alluvium. Penmynydd. Height one foot.

(Figure 57) Polyclinal minor folding. 300 yards south-west of Ty'n-y-mynydd-east, Mynydd Llwydiarth. East side of slack. Height about two inches.

(Figure 58) Polyclinal minor folding. 250 yards south by west from Ty'n-y-mynydd-east. Height one foot.

(Figure 59) Polyclinal minor folding. 250 yards west of Ty'n-y-mynydd-east, south of dry pool. Height three feet.

(Figure 60) Detail at top of (Figure 59).

(Figure 61) Plan of five-foot folds in hornblende-schist. About 100 yards north-east of Gigfran, Mynydd Llwydiarth.

(Figure 62) Minor thrusts in the Tre-Arddur zone. Cliffs west of Castell.

(Figure 63) Minor thrusts in the Tre-Ardour Zone. Foot of crag, south-east of Gareg-fawr. Height about nine inches.

(Figure 64) Sigmoidal foliation with thrusts at one-foot intervals. East bluffs of Trwyn Bychan.

(Figure 65) Structures in the Amlwch Beds. (a) West-south-west of Graig-ddu. (b) Porth-y-gwartheg. (c) About 250 yards west-north-west of 'Cave', Bull Bay.

(Figure 66) Structures the Amlwch Beds. Porth-y-gwartheg.

(Figure 67) Incipient lenticular cutting. 170 yards north-east of Coast-guard path end, Analweh. Half natural size.

(Figure 68) Breaking down of Tyfry Beds. One-third natural size. 400 yards west by north from Tyfry.

(Figure 69) Diagram of autoclastic melange.

(Figure 70) Strain slip. Quarter of a mile west of Minffordd Windmill

(Figure 71) Change of structure along the estuary of the Alaw. Amplitudes one foot or less. Nos. a to e in order eastwards, from Valley Foundry to Gored Footpath.

(Figure 72) The valley thrust-planes. Crags above the railway, east and south-east of Llanfair-yn-neubwll Church.

(Figure 73) The valley thrust-planes. Further stage, and with vein-quartz. Crags above the railway. east and south-east of the same Church.

(Figure 74) Undulations o' the valley thrust-planes.

(Figure 75) The folding and thrusting of the valley thrust-planes. Amplitudes up to four feet. Crags above the railway, north-east and east of the Church.

(Figure 76) Diagram to illustrate the change from isoclines of Holy Isle into the foliation of the Western Region.

(Figure 77) Folded phacoids of grit. 300 yards east-north-east of Pedair-groeslon.

(Figure 78) Limestones in Gwna Green-Schist. Baron Hill drive, at 'M' of 'Meurig'. Height about 15 feet.

(Figure 79) Folded phacoid of limestone in (Figure 78), Longest limb about two feet.

(Figure 80) Cross-wrenches. (a) Bodewran. (b) North side of road 550 yards west of Garth Ferry Inn.

(Figure 81) Foliation in a grit. West of Forth Rutrydd. Height 30 feet.

(Figure 82) Foliation in grits of South Stack Series. Quarry north of road. Kngsland. Holyhead.

(Figure 83) foliation in grits. East of Porth Ruffydd.

(Figure 84) Diverging foliation in grit. Amplitude about two feet. Headland west-south-west of Gors-goch,

(Figure 85) Porth Ruffydd Bending of foliation in fold of bedding.

(Figure 86) Folding of foliation of fissile bed at junction with overlying grit. Cliff north·north·east of Maen·y·fran, Rhoscolyn.

(Figure 87) Foliations in a two-inch anticline Rhoscolyn

(Figure 88) Minor structures at the end of the South Stack

(Figure 89) Folding of foliated minor thrust-planes. With truncation of bedding. Headland three-sixteenths of a mile east of Clybyddiad. Height, about two feet.

(Figure 90) Second foliation crossing three foot isocline of glaucophane-schist in mica-schist Farm north-east of Tyddyn-fawd.

(Figure 91) Major folds of the quartzite on the great sea cliffs. Bedding obscure where lines are dotted. Height, about 500 feet.

(Figure 92) Diagram Breakwater Fold. HQ=Holyhead Quartzite. SSS=South Stack Series. BT=Breakwater Thrust-plane. G=Direction of gape of Holyhead Fold.

(Figure 93) Section across the Breakwater Tract. About three-eighths of a mile east of Porth Namarch. Scale 24 inches = one mile. HQ = Holyhead Quartzite. SMB = Stack Moor Beds. LB = Llwyn beds. CB = Celyn beds. SPB = Soldier's Point Beds. TT = Thrust

(Figure 94) Section at Mynachdy. Scale: Nine inches = one mile. MN = Amlwch Beds. MG = Gwna Beds. M = Gneiss. beb = Lower Ordovician Beds. be = Glenkiln Beds. CT = Caerau Thrust-plane. MyT Mynachdy Thrust-plane. WT = Wig Thrust-plane. CHT = Carmel Head Thrust-plane.

(Figure 95) The thrust-planes at Trwyn Bychan. Sketched from a boat. Cliffs about 100 feet in height. MS = Church Bay Tuffs. MG = Gwna Melange. b = Nemagraptus Shales.

(Figure 96) The Wylfa Thrust-Plane, Porth Wnol. Cliff about 80 feet in height. MG = Gwna Mélange. MN = Amlwch Beds.

(Figure 97) Diagram of supposed original relations of Glenkiln Conglomerates to the Mona Complex in the Gynfor District, b'= Pale conglomerate. b = Purple conglomerate. MQ = Gwna Quartzite.

(Figure 98) Strike, dip, overfolding, and pitch in the Aethwy region. Scale: Six miles = one inch. Broken line junction of Penmynydd Schist and Gwna Green-schist. Long-tailed arrows = Pitch.

(Figure 99) The major secondary folds on the main island. XX = Top of New Harbour Beds. CHT = Carmel Head Thrust-plane. CS = Caradog Syncline. BA = Bodafon Anticline. BS = Bodwrog Syncline. BT = Bodorgan Thrust-plane, BA = Plâs-bach Anticline. HA = Hermon Anticline. BF = Berw Fault. LW = Llanddwyn Wedge. NS = Newborough Slide. AA = Aethwy Anticline. LS = Llanddona Synclinorium.

(Figure 100) Chart showing the distribution of the tectonic horizons of the Mona Complex. Scale: 1 inch = 6 miles.

(Figure 101) a. Chart showing the general directions of strike and other structures in the Mona Complex. Scale: 1 inch = 6 miles. 101B Chart showing the distribution of the metamorphism in the Mona Complex. Scale: 1 inch = 6 miles. BS. LM. = Bedded Succession, Low Metamorphism. BS. HM. = Bedded Succession. High Metamorphism. PI. & H. = Plutonic Intrusions and Hornfels. Gn. Gneisses. Note: To bring out the waxings and wanings. delicate gradations of stipple would be required that could not he applied to a small-scale chart. The chart here given ignores all gradation, and minor complications, but shows at a glance the general distribution of the metamorphism.

(Figure 102) Pebbles from the basal Arenig conglomerates Containing old folds and thrusts of the Mona Complex. 102 B. Pebble from Lower Cambrian Grits containing an old fold and vein of the Mona Complex.

(Figure 103) Deflection of the Scolithus pipes.

(Figure 104) Nipped 'galls' in the grits on the steps above The South Stack.

(Figure 105) North cliff of Henborth.

(Figure 106) Thin siliceous seams and fissile seams. Specimen from near Gors-goch.

(Figure 107) Major and minor isoclines in Llwyn Beds. Cliff looking north from Penrhyn-mawr.

(Figure 108) Minimum folds on limb of minor fold. About one-eighth of a mile south- west of Porth Ruffydd.

(Figure 109) Second foliation in new harbour beds. Tre-Arddur.

(Figure 110) Outlier from thrust at 'H' of 'Holy' Holyhead. Height: about 30 feet.

(Figure 111) South Stack Series, With anticline of Passage Beds. North-west of Stryd.

(Figure 112) Passage Beds. South-west of Millbank Gardens; north of 't' of 'Stryd'. With infolds of South Stack Series.

(Figure 113) Section quarter-mile south-west of Capel Gorllas. Scale: 18 inches = one mile. SSS = South Stack Series. ST = Spilitic Tuff. MN = New Harbour Beds.

(Figure 114) Bedding in the quartzite at the North Stack. Height, about 100 feet.

(Figure 115) Folding against dip at Penrhos.

(Figure 116) Second foliation Soldier's Point. About one foot.

(Figure 117) Isoclines in fissile bed in Stack Moor Beds. Overfolding contrary to dip.

(Figure 118) section along Porth Namarch. Height of cliff: 50–60 feet. HQ = Holyhead Quartzite. BC = boulder-clay. SSS = South Stack Series. BT = Breakwater Thrust-plane. Nf = Namarch Fault.

(Figure 119) Porth Namarch. Section at right angles to (Figure 118), at x.

(Figure 120) Detail of the Breakwater Thrust-plane. From (Figure 119).

(Figure 121) the Rhyd-Bont creek intrusions. From the six-inch map. Reduced from the .0004 maps. MN = New Harbour Beds. U = Serpentine. E = Gabbro.

(Figure 122) The Cerig-Moelion intrusions and the Garan Thrust-plane. From the six-inch map. Reduced from the .0004 map. MN = New Harbour Beds. U = serpentine and ophicalcite. E = gabbro in ring dykes.

(Figure 123).-Northward thrusts, Porth-y-defaid. Height: about six feet.

(Figure 124) Minor folding, north end Llyn Llywenan.

(Figure 125) Curved and folded valley thrust-planes. Penllyn, Llyn Llywenan.

(Figure 126) Undulating foliation-dip.

(Figure 127) Small thrusts in quartz-vein. Alaw Ravine. Boss in alluvium east of Stryd-y-facsen. Two-thirds natural size.

(Figure 128) Minor folding. Low type. Meiriogen.

(Figure 129) Small thrusts in one-foot fold. South-west of Porth Trwyn.

(Figure 130) Section across the two coves at Porth-yr-hwch. M= granitoid gneiss. MF = Fydlyn Beds. MG = Gwna Mélange, with limestone. b = Ordovician shale. Height at north end: about 200 feet

(Figure 131) Northern part of the Gader Inlier. Scale = two-thirds of .0004 (1/2500) map. Granite sills in gneiss.

(Figure 132) minor folding in Coeden Beds. a. Tarn east of Llanfflewyn Church. b. South of 'h' of 'Mechell'. c. Mynydd Mechell, north side. d. Mynydd Mechell, north side. e. Slope opposite Geirian spoil-bank. f. Mynydd Mechell.

(Figure 133) Epidosite bands. Henborth.

(Figure 134) Jaspers and spilites in Amlwch Beds. Coast near coastguard path end Amlwch. From the .0004 (1/2500) maps.

(Figure 135) Isoclinal folding in Amlwch Beds. Behind rectory, Llanfairynghornwy. [Matley.]

(Figure 136) Folded jaspers in Amlwch Beds. On Amlwch Port Moor. From the .0004 or 1/2500 maps.

(Figure 137) Shears in Gwna Quartzite. Graig-wen.

(Figure 138) Nine-inch bedded autoclast. Llanbadrig.

(Figure 139) North-west cliffs of Mynydd Wylfa. From the 1100-1 or 1:2500 map. MG=Gwna Mélange. Qt=Gwna Quartzite. G=Granite.

(Figure 140) Thrust north of Ogo Gynfor. Cliff about 100 feet.

(Figure 141) Detail at the Trwyn Bychan Thrust-Plane.

(Figure 142) Quartzite pebble bisected along foliation of tuffs. Trwyn Bychan.

(Figure 143) Thrusts cutting foliation. The Skerries.

(Figure 144) Small granitoid sills in the Gneiss. A few yards north of Porth Helygen.

(Figure 145) Granite sills in Mica-hornfels. Heights on south side of main road, quarter to half a mile west of Caer-glaw. Lengths: a. six feet ; b, c, ten feet.

(Figure 146) Four-inch granite sill in Mica-hornfels. Same locality as (Figure 145).

(Figure 147) Granite sills in an inclusion of Mica-hornfels. Length: two to three feet. Same locality as (Figure 145).

(Figure 148) Six feet of granite vein in Mica-hornfels. Same locality as fig. 145.

(Figure 149) Four-foot plan of granite sills in Mica-hornfels. Werthyr bend of river Caradog.

(Figure 150) Six-inch granite sill in hornfels. Gwalchmai, 250 yards north of inn.

(Figure 151) Ten inches of bedded Mica-hornfels truncated by granite. Laneside, west of y-foel.

(Figure 152) Granite sills in Hornblende-hornfels. Maen-gwyn Farm, at 'oed' of 'Coedana'.

(Figure 153) Transgressive margin of granite. Maen-gwyn.

(Figure 154) Northern parts of Bodafon Moor. From the six-inch maps. M = Bodafon Moor Schist. MQ = Bodafon Quartzite. b= Ordovician Shale. c = Old Red Sandstone.

(Figure 155) The central parts of Mynydd Bodafon. From the six-inch maps. M = Bodafon Moor Schists. MQ = Bodafon Quartzite. C = Old Red Sandstone.

(Figure 156) Section across Bodafon Moor and the northern .summit of Mynydd Bodafon. Scale: Eight inches = one mile. Symbols: M = Bodafon Moor Schist. Q = Bodafon Quartzite. b= Ordovician Shale. c = Old Red Sandstone.

(Figure 157) Section through the central parts of Mynydd Bodafon. Scale: Eight inches = one mile. Symbols: M = Bodafon Moor Schist. Q = Bodafon Quartzite. b= Ordovician Shale. c = Old Red Sandstone.

(Figure 158).-Section through the southern parts of Mynydd Bodafon. Scale: Eight inches = one mile. Symbols: M = Bodafon Moor Schist. Q = Bodafon Quartzite. b= Ordovician Shale. c = Old Red Sandstone.

(Figure 159) Late thrusts of Ynys Meibion. height: about nine feet.

(Figure 160) The Bodwrog Marble. From the six-inch maps. G = Coedana Granite. M = Mica-schist. D = Palaeozoic Dyke. [alluvium symbol] = Cors Bodwrog  Alluvium.

(Figure 161) Large quartzite in Gwna Mélange. (several yards high.) 300 yards north-west of Porth Cadwaladr.

(Figure 162) Folding and cleavage. ×½ Tyfry Bed Blocks from Bodorgan Tunnel.

(Figure 163) Foliation crossing jasper. 200 yards west-north- west of Prys-iorwerth.

(Figure 164) Folding of a Lower Engan Spilite. Craig-lâs. Five feet high.

(Figure 165) Base of limestone. South-west of Pen-y-parc, at Bath House, Menai Strait. Height: about 10 feet.

(Figure 166) Limestones in Gwna Green-schist. About four feet and three feet thick. Roadside, about 200 yards west of bathing house.

(Figure 167) Basic schist in Gwna Green-schist. 500 yards west of Garth Ferry Inn. Height: about four feet.

(Figure 168) Eastern side of quartzite, Pen-y-parc. Height: about 10 feet.

(Figure 169) Lenticular quartzite. Three and a half feet long. In Gwna Mélange, Llansadwrn.

(Figure 170) Basic knot in Gwna Green-schist. 250 yards west of Ty'n-y-mynydd-east.

(Figure 171) Basic schist crossing the strike. About four feet.

(Figure 172) Section and plan of basic and acid schist. Height: about six feet. 460 yards north-north-west of Ty'n-y-mynydd-east.

(Figure 173) Chlorite-epidote-schist in Gwna Green-schist. Foliation-dip counter to true dip. 250 yards south-west of Ty'n-y-mynydd-east. Height: about one foot.

(Figure 174) Biotite-augen. Gored Islet.

(Figure 175) Cross-folds in Glaucophane-schist. Castellior.

(Figure 176) Hornblende-schist on Mica-schist. Three-sixteenths of a mile south-west of Rhos-gerig.

(Figure 177) Quartz-vein In fault, crossed by foliation of Glaucophane-schist. Farm north-east of Tyddyn-fawd.

(Figure 178) Llangaffo cutting. Hornblende-schist and Diorite shaded, Mica-schist unshaded.

(Figure 179) Folding at Treferwydd.

(Figure 180) Sharp small fold on foliation-dip of mica-schist.

(Figure 181) Venous-quartz phacoids In Mica-schist. Near Berw.

(Figure 182) Three-inch vein-quartz lenticle truncating vein-quartz seams. Near Berw.

(Figure 183) Internal corrugation in folded siliceous seam a few inches thick. Bridin Farm-yard

(Figure 184) Basic and Acid Schist. 417 yards south-west of Careg-landeg. 10 feet by 1 foot.

(Figure 185) The southern parts of Mynydd Llwydiarth. From the six-inch maps. Eastern summit at the 500-foot-contour. MG = Gwna Green-schist. M = Penmynydd Mica-schist. Mhb = Hornblende-schist. MGl = Glaucophane-schist. Gl-Di = Glaucophane-Diorite. D = Palaeozoic dolerite dykes. [Alluvium symbol]= alluvium. RR = the diverging pair of Ruptures. The symbols indicate dip, isoclines and pitch, all of foliation.

(Figure 186) Isoclines of about three-foot amplitude in Glaucophane-schist. South-east of Gigfran.

(Figure 187) Five-inch pegmatite-vein in Gwna Green-schist. Newborough, 280 yards north-west of Tir-Forgan.

(Figure 188) 1/2500-plan of boss at Cerio-duon, Newborough. Spilite-schist, limestone, quartzite, and Gwna Green-schist.

(Figure 189) Third boss on Baron Hill Drive. Scale: one inch = 50 feet.

(Figure 190) Fourth boss on Baron Hill Drive. Scale: one inch = 50 feet.

(Figure 191) Face of cliff. Two and three-quarter inches below the thrust shown under x in (Figure 189) Natural size.

(Figure 192) Bedding and cleavage on Careg-onen beach.

(Figure 193) Spicules of the Careg-onen Beds. Simple forms from Careg-onen. Hexactinellid from Coch-y-mieri. × 12.

(Figure 194) Section along the cliffs at Careg-onen. Scale: one inch = 440 feet. Gwna Green-schist (a); Careg-onen Beds (b); Ordovician Shales (c); Carboniferous Limestone (d).

(Figure 195) The anticline at × in (Figure 194)  [Section along the cliffs at Careg-onen]

(Figure 196) Detail of (Figure 195).  [Section along the cliffs at Careg-onen]

(Figure 197) Detail of (Figure 195). [Section along the cliffs at Careg-onen]

(Figure 198) Sketch section of Careg-onen beds at Coch-y-mieri.

(Figure 199) Sketch section. About a quarter of a mile south-west of Ty-mawr. M = Penmynydd Schists. a = Careg-onen Beds. b = Ordovician Shales.

(Figure 200) Spicules of Glenkiln Chert, Porth wen. × 12.

(Figure 201) Section across the Ordovician rocks of Llangwyllog. Scale 8 inches = 1 mile. M = Penmynydd (Mona) Schists. b = Ordovician (Undifferentiated) be = Extensus Zone (With basal grit) Fe = Oolitic Ironstone. Bg = Gracilis Zone.

(Figure 202) The complex at Llyn Traffwll. Scale .0004 or 1:2500. M = Gneiss. Mhb = Basic Gneiss. G = Granite. MN = New Harbour Beds. be = Conglomerate of Extensus Zone. D = Diabase. [Alluvium symbol]= Lacustrine Alluvium.

(Figure 203) The rupture at Yr-ogo-goch. Height about 100 feet.

(Figure 204) section across Foel Hill, Llanerchymedd. Scale-12 inches = one mile. M Mica-schist and u = Hornfels, Mona Complex. bh = Zone of Did. hirundo. be = Zone of Did. extensus (with basal conglomerate)

(Figure 205) North-westward facing isoclines in Arenig Beds below the Bodafon Thrust-plane. Height six feet and two feet. Bend in stream mile east of Llwydiarth Esgob.

(Figure 206) North-westward facing isoclines in Arenig Beds below the Bodafon Thrust-plane. Height six feet and two feet. Bend in stream mile east of Llwydiarth Esgob.

(Figure 207) The Fferam Infold. Six inches = one mile. Symbols as in (Figure 208) [MG = Gwna (Mona) Schists. Be = Zone Of Did. extensus (with basal conglomerate) Bb = Zone of Did. bifidus. bm = Zone of Did. murchisoni. Fe = Oolitic Ironstone. Bg = Zone Of Nem. gracilis.]

(Figure 208) Section across the Fferam Infold, Llanbabo. Scale-12 inches = one mile. MG = Gwna (Mona) Schists. Be = Zone Of Did. extensus (with basal conglomerate) Bb = Zone of Did. bifidus. bm = Zone of Did. murchisoni. Fe = Oolitic Ironstone. Bg = Zone Of Nem. gracilis.

(Figure 209).-Ironstone and Gracilis Shales at the Lane Infold.

(Figure 210) The Church Infold. Six inches = 1 mile. Symbols as in (Figure 211) [Be = Zone of did. extensus (with conglomerate) bb = zone of Did. hirtindo. bb = Zone of Did. bifidus. bm = zone of Did. murchisoni. Bt = Zone of Glypt. teretiusculus. bg = Zone of Nem. gracilis. be = Zone of Dicran. clingani.]

(Figure 211) Section across the Church Infold, Llanbabo. Scale-12 inches = 1 mile. Be = Zone of did. extensus (with conglomerate) bb = zone of Did. hirtindo. bb = Zone of Did. bifidus. bm = zone of Did. murchisoni. Bt = Zone of Glypt. teretiusculus. bg = Zone of Nem. gracilis. be = Zone of Dicran. clingani.

(Figure 212) The Rhwnc Thrust-plane at Rhwnc. Height about 10 feet. F = Sheared felsite. b = Arenig shales.

(Figure 213) Section through the west end of Parys Mountain. Scale eight inches = one mile. bhb = Phyllograptus and adjacent Shales. bcp = Hartfell Shales. bv = Llandovery Shales F = Felsite. CT = Chapel Thrust-plane. RT = Rhwnc Thrust-plane.

(Figure 214) Section through the central parts of Parys Mountain. Scale 7.5 inches = one mile.  MN = Amlwch Beds, Mona Complex,  M=Gneiss, Mona Complex  Be = Zone of Did. extensus.  bb = Zone of Did. bifidus.  bc = Zone of Dicran. clingani..  bp = Parys Green shales.  bv = Llandovery Shales.  bvʹ = Tarannon shales.  F = Felsite.  Cl = Charlotte's Lode (on strike of north discovery lode)  Cdl = Careg-y-doll lode.  NT = Nebo Thrust-plane.  RT = Rhwnc Thrust-plane.  CHT = Carmel Head Thrust-plane.

(Figure 215) The Craig-y-gwynt Anticlines.

(Figure 216) Generalised section through Mynydd Eilian. Scale-7 5 inches = one mile. MN = Amlwch Beds, Mona Complex. M =Gneiss, Mona Complex. CHT = Carmel Head Thrust-plane. be = Zone of Did. extensus (with conglomerate) Bb = Zone of Did. bifidus. bt = Zone of Glypt. teretiusculus. F = Felsite, bg-c = Glenkiln-Hartfell Passage beds.  bp = part's green shales.  by = Llandovery.

(Figure 217) Section through Torllwyn and Graig-wen. Scale-16 inches = one mile. MG = Gwna grit and phyllite, Mona Complex. GQ Gwna quartzite, Mona Complex. CS = Cherty Shales. Glenkiln. GC = Grey conglomerate, Glenkiln. PC =Purple conglomerate, Glenkiln.

(Figure 218) North-west cliff of Llanlliana Head. Sketched from a boat. Height about 100 feet. Glenkiln conglomerate and cherty shales.

(Figure 219) Bluff about 200 feet high. About 200 yards east of Glochog. Glenkiln conglomerate and cherty shales.

(Figure 220) Cliff section at Ogof Gynfor. Drawn from a boat, and brought to one plane. Scale about 65 feet = one inch. MG = Gwna mélange. MGʹ = Gwna quartzite. Mgʺ = Gwna limestone. b = Glenkiln conglomerate. bʹ = cherty shales. Graptolites [a.f. 3507-22] obtained from base of shales below X. Unconformable base (see (Plate 29) and (Figure 221)) well seen at cliff's foot below O.

(Figure 221) The unconformable junction of (Plate 29).

(Figure 222) Section through the Ordovician Infold of Mynachdy. Scale eight inches = one mile. MN = Amlwch Beds. MG = Gwna Beds. bg = Glenkiln shales, with limestone and conglomerate. MT = Mynachdy Thrust-plane. PS = Padrig slide.

(Figure 223) Six-foot limestone lump in gracilis beds. North cliff of Porth Padrig.

(Figure 224) The Porth Padrig slide. Height about 30 feet.

(Figure 225) Second injection (3–4 inch thick) in dolerite dyke. Menai strait, east of Pen-y-parc.

(Figure 226) Dolerite dykes crossing Mynydd Mechell. From the six-inch map.

(Figure 227) Basic dykes at Penrhyn, Cemaes. From the .0004 (1:2500) maps.

(Figure 228) Margin (6 inches) of small dolerite dyke, Menai Strait.

(Figure 229) One-foot vein from dyke in Cemaes Bay.

(Figure 230) 3-inch dyke near Garth Lodge Gate. 125 feet north-east of '67'.

(Figure 231) Part of margin of dyke. Shore south of Garth Lodge.

(Figure 232) Splitting of the Bhoscolyn dyke. Scale: .0002 or 1: 5000.

(Figure 233) 13-foot dyke of (Plate 30).

(Figure 234) group of small (six to 12-inch) dykes. Menai Strait, east-south-east of Pen-y-parc.

(Figure 235) Large dyke. Quarter of a mile east-south-east of Llyn Bwch.

(Figure 236) Six-inch dyke. 286 yards south-south-east of Llanddygfael-hir.

(Figure 237) Two-foot dyke. Three-eighths of mile north of west of Bwlch.

(Figure 238) Felsite dyke, Ynys-fawr. Nine yards wide.

(Figure 239) Flank of felsite Dyke. Group south-west of Gwalchmai.

(Figure 240) Felsite dyke. 270 yards west-north-west of Gwalchmai Inn.

(Figure 241) Felsite dykes. South-west of Gwalchmai. From the six-inch map.

(Figure 242) Felsite sheet with Granite outlier at Bryn Twrog. From the six-inch map.

(Figure 243) Felsite, dolerite, and compound dykes. North of Coeden. From the six-inch map.

(Figure 244) Felsite, dolerite, and compound dykes at Drum. From the six-inch map.

(Figure 245) Intrusions on Mynydd Eilian. From the six-inch map. MG = Gwna Mélange. b = Ordovician. F = Felsite. U = Hornblende-picrite. D = Proterobase. Cross-hatched lines = roads.

(Figure 246) Small basic sills at Llandyfrydog.

(Figure 247) Faulted basic sill at Llanerchymedd Station. Not measured, but height about 20 feet.

(Figure 248) Sill of diabase in Llanvirn Shales. 166 yards north-east of bathing house, Dulas Bay. Height, 15 feet.

(Figure 249) Tongues from basic sill. Ogo-fawr.

(Figure 250) Basic sill on lighthouse crag, The Skerries. Height about 20 feet.

(Figure 251) Felsite sill. 70 yards south of Ogo-fawr. Height about 60 feet.

(Figure 252) Shift of margin of basic sill, Ogo-fawr.

(Figure 253) Thrust in dyke at Pant-howel. Height about 20 feet.

(Figure 254) A few inches of the northern margin shown in (Figure 253).

(Figure 255) Plan (2½ feet long) of shifts in dolerite dyke at Careg Lydan.

(Figure 256) Schistose dyke at Gwalchmal Seven-sixteenths of mile north-east of Caer-glaw.

(Figure 257) Shifted one-foot Dyke. North cliff of Porth Tre-castell.

(Figure 258) Dolerite on coast west of Careg-onen.

(Figure 259) Two-foot schistose Dyke. Eastern cliff of Point Lynas.

(Figure 260) Section in the composite dyke West of Llanpechell. (Matley.) Width shown = about 16 feet. 1 = Felsite. 2 = Dolerite.

(Figure 261) Folding, thrusting, and cleavage on the foreshore at Rhosneigr. Amplitudes about one foot.

(Figure 262) Folding, thrusting, and cleavage on the foreshore at Rhosneigr. Amplitudes about one foot.

(Figure 263) Folding, thrusting, and cleavage on the foreshore at Rhosneigr. Amplitudes about one foot.

(Figure 264) The Nebo Thrust-plane on the coast. M = gneiss. b bifidus shales. Height: about 20 feet.

(Figure 265) Detail of (Figure 264) Height: about one foot.

(Figure 266) The Gwichiaid Slide at the sea-cliff, with thrust-planes in folded shales. Height: about 30 feet. X= gneiss. b Llanvirn shales.

(Figure 267) Minor thrusts in shale. Porth y gwichiaid beach. Height about 10 feet.

(Figure 268) Horizontal thrust in shale. North cliff of Porth y gwichiaid. Height: about 10 feet.

(Figure 269) Outcrop of the Carmel Head Thrust-plane at Gwaen-ydog. From the six-inch maps. MH = Coeden beds. MG = Gwna Beds. b = Arenig Beds. F = Felsite Dykes. D = Dolerite Dykes. K = Crushed Dykes.

(Figure 270) The Carmel Head Thrust-plane at Carmel Head. MN = Amlwch Beds. b = Cleaved Ordovician Shale.

(Figure 271) Minor thrusts at the Carmel Head Thrust-plane, Carmel Head. Depth: about one foot. ChT = The Main Thrust.

(Figure 272) The Carmel Head Thrust-plane, 147 yards south-west of Llanfairynghornwy Church. Height: about eight feet. MG = Gwna Beds. b = Ordovician Beds.

(Figure 273) Folding and cleavage in Arenig Shale with Grits from 3 to 12 inches thick. Foreshore at Rhosneigr.

(Figure 274) Shredding of Arenig Beds along cleavage. Rhosneigr Shore.

(Figure 275) Section through the Old Red Series from Coed-y-gell to Lligwy Bay. Scale: eight inches = one mile. Symbols used M = Bodafon Moor Schists, Mona Complex, Mq = Bodafon Quartzite, Mona Complex. b = Ordovician. c = Old Red Sandstone Series. c = cornstones d = Lligwy Sandstone d2ʹ = D1 Subzone of Carboniferous Limestone. d2ʺ D2 Subzone of Carboniferous Limestone. BT = Bodafon Thrust-plane.

(Figure 276) Section from the north end of Bodafon Moor, through the Old Red Series, to the Smithy. Scale: eight inches = one mile. Symbols used M = Bodafon Moor Schists, Mona Complex, Mq = Bodafon Quartzite, Mona Complex. b = Ordovician. c = Old Red Sandstone Series. c = cornstones d = Lligwy Sandstone d2ʹ = D1 Subzone of Carboniferous Limestone. d2ʺ D2 Subzone of Carboniferous Limestone. BT = Bodafon Thrust-plane.

(Figure 277) Section from the northern summit of Mynydd Bodafon, across the Vale of Lligwy. Scale: 7.5 inches = one mile. Symbols used M = Bodafon Moor Schists, Mona Complex, Mq = Bodafon Quartzite, Mona Complex. b = Ordovician. c = Old Red Sandstone Series. c = cornstones d = Lligwy Sandstone d2ʹ = D1 Subzone of Carboniferous Limestone. d2ʺ D2 Subzone of Carboniferous Limestone. BT = Bodafon Thrust-plane.

(Figure 278) section parallel to part of (Figure 276), along a line 266 yards further to the west-north-west. Scale: 8 inches = 1 mile. Symbols used M = Bodafon Moor Schists, Mona Complex, Mq = Bodafon Quartzite, Mona Complex. b = Ordovician. c = Old Red Sandstone Series. c = cornstones d = Lligwy Sandstone d2ʹ = D1 Subzone of Carboniferous Limestone. d2ʺ D2 Subzone of Carboniferous Limestone. BT = Bodafon Thrust-plane.

(Figure 279) Wedging out of small cornstones. Porth-y-môr.

(Figure 280) Section about a mile north-east of Llangefni. Scale: 12 inches = one mile. MG = Gwna Mélange. C = Old Red Sandstone. d2 = Lligwy Sandstone (Carboniferous) d2 = Carboniferous Limestone.

(Figure 281) Contemporaneous contortion in old red sandstone. Traeth-yr-ora.

(Figure 282) Isoclinal anticline in Old Red Sandstone. Lligwy Bay.

(Figure 283) Isoclinal syncline in Old Red Sandstone. Lligwy Bay.

(Figure 284) Thrusting in old red sandstone. Lligwy Bay.

(Figure 285) (a–e) The turning of the cleavage round the monoclinal fold in the Old Red Series. Coast between Porth-y-môr and Lligwy Bay.

(Figure 286) Lumps in Limestone conglomerates.

(Figure 287) Lumps in Limestone conglomerates.

(Figure 288) Anomalous junction at Borth-wen, Benllech.

(Figure 289) The succession at Trwyn-dwlban. (piped limestone, pipe-sandstone, shale, upper limestone.)

(Figure 290) Floor of sandstone pipe at Porth-yr-aber.

(Figure 291) Section through the contemporaneous disturbance and the Lligwy Bay conglomerate, Careg-ddafad. Scale: one inch = 75 feet.

(Figure 292) Section at Porth-y-forllwyd. Scale One inch = 75 feet.

(Figure 293) Generalised section from Lligwy Bay through Morlfre Point. Scale eight inches = one mile. LBC = Lligwy Bay conglomerate. RCL = Royal Charter limestone. HS = Helaeth sandstone. ML = Moelfre limestone.

(Figure 294) Section along the coast from Penrhyn to Benllech. Scale nine inches = one mile.

(Figure 295) Castell-mawr, Red Wharf Bay. Scale nine inches = one mile.

(Figure 296) Section across the Graig-fryn inlier and the vale of Lligwy. Scale eight inches = one mile. MQ = Bodafon Quartzite. C = Old Red Sandstone. dʹ2, dʺ2 = D1 and D2 sub-zones of Carboniferous Limestone

(Figure 297) Carboniferous outlier at Glan-aber, Llangefni.

(Figure 298) The Carboniferous Limestone resting on the Mona Complex. Railway cutting, Bodorgan.

(Figure 299) Section through the Strait-side Carboniferous area, from the Trefwri outlier to the Menai Strait. Scale eight inches = one mile. M = Mona Complex. ds = Carboniferous Sandstone. d2ʺ = Carboniferous Limestone.

(Figure 300) Carboniferous base at Plâs Llanfair. Scale eight inches = one mile.

(Figure 301) Section along the coast from the Penmon Quarries to the east point of Anglesey. Scale-16 inches = one mile. d2ʺ,d2‴ = D2, D3, sub-zones of Carboniferous Limestone.

(Figure 302) section across the Anglesey coalfield from Lledwigan to Berw. Scale eight inches = one mile. M = Penmynydd Schists, Mona Complex MS = Tyfry Beds Mona Complex  d2‴ = Carboniferous Limestone. dp = Posidonomya Cherts. d4 = Millstone Grit d5 = Coal Measures. 1, 2, 3, 4, 5, 6, 7 = Coal Seams. d6 = Red Measures.

(Figure 303) Base of Millsone Grit at Bodorgan. Height of old cliff about 10 feet.

(Figure 304) Polyzoon from pebble in Red Measures. × 12.

(Figure 305) Folding at the Berw Fault, Ceint. (after Henslow.)

(Figure 306) Junction of a Palaeozoic and a later dyke near Gaerwen. Scale: one inch = about 15 feet. M = Penmynydd mica-schist. D = Palaeozoic dyke. Dʹ= later dyke.

(Figure 307) Glacial furrow at Amlwch port.

(Figure 308) Deflect ed glacial stride at Trwyn-dwlban.

(Figure 309) Profile, of undercut furrow, Trwyn-dwlban. About natural size.

(Figure 310) Undercut shelf, with boulder-clay, Felin-wen.

(Figure 311) Undercut shelf, Six feet in height, with boulder-clay, Huslan cliff.

(Figure 312) Ice-moulded sea-cliff near Aber-cawell. Height about 50 feet.

(Figure 313) Glacial disruption and thrusting at Porth-delisc. Height about one foot.

(Figure 314) Glacial disruption and dragging-out at Porth-delisc. Length about six feet.

(Figure 315) Boulder-clay driven under dolerite, near Plâs-bach. Depth about five feet.

(Figure 316) Boulder-clay on the top of a boss of dolerite, near Plâs Maelog.

(Figure 317) Boulder-clay filling two-foot hollow on boss: about quarter of a mile east of Bodior.

(Figure 318) Boulder-clay on summit of boss: about three-quarters of a mile east of Castell Eden.

(Figure 319) Boulder-clay between bosses: Llyn Badrig.

(Figure 320) Boulder-clay on slope of boss: near Rhytty.

(Figure 321) Penial Drum.

(Figure 322) Llanfachraeth Drum.

(Figure 323) Clymwr Drum.

(Figure 324) Drumlins near valley. Scale: two miles = one inch.

(Figure 325) The path of the ice. Scale: one inch = eight miles.

(Figure 326) The principal boulder-trains. Scale: one inch = eight miles.

(Figure 327) The Carboniferous limestone of Bryn-gwallen. From the six-inch map.

(Figure 328) Glacial gravel and sand, with boulder-clay. Penrhos Beach, Holyhead.

(Figure 329) Section in Penrhos Drum.

(Figure 330) Glacial gravel and sand at Ty-gwyn, Llangefni.

(Figure 331) Rhydgroes and Werthyr Drums.

(Figure 332) The drumlins of the northern valley. Scale: one inch = two miles. High driftless ridges dotted. 1. Cemaes Drum. 2. Dymchwa Drum. 3. Pen-y-morwydd Drum. 4. Bodewryd Drum 5. Ysgellog Drum. 6. Oriw Drum. 7. Rhyd-groes Drum. 8. Hafod-llin Drum. 9. Werthyr Drum. 10,10 Nant-y-frân Drums. 11. Carog Drum. 12. Llanfairynghornwy Drum.

(Figure 333) Boulder-clay bluffs in Bull Bay. Height about 100 feet.

(Figure 334) Buried escarpment at Croes-fryn.

(Figure 335) Glacial gravels, Ty'n-y-caeau, Menai Bridge.

(Figure 336) The gravel of, Porth-Dafarch.

(Figure 337) The exit of Cremlyn. Scale four inches = one mile.

(Figure 338) Sketch-map of the sea-floor. d2 = Carboniferous Limestone. f = Triassic rocks. dp = Posidonomya Cherts. g = Jurassic rocks. d5 Coal Measures. h = Cretaceous.

(Figure 339) Holyhead Mountain, from Rhoscolyn, and the South Stack Moor: sketched from the Bwa Gwyn, Rhoscolyn.

(Figure 340) Stages of the Menai Strait. Scale: four miles = one inch. 1. Pre-glacial. 2. Late-glacial. 3. Post-glacial. W R = Western Reach. M R = Middle Reach. R = Eastern Reach. I D = Ice-Dam.

(Figure 341) Undercut sea-cliff, Trwyn-dinmor.

(Figure 342) Post-glacial marine erosion: coast near Trwyn-bychan.

(Figure 343) The Coal Measures at Berw. Scale: four inches = one mile.

(Figure 344) Shaft and boring sections. Bymrs. Greenly. Scale: one inch = 200 feet.

(Figure 345) Index-chart to the solid-geology' maps. Scale one inch = six miles.

(Figure 346) Index-chart to the ' drift ' maps. Scale one inch = six miles.

Plates

(Plate 1) The Folding of the Mona Complex, as viewed from the South Stack, Holyhead. Height seen: 445 feet. Frontispiece to Vol 1..

(Plate 2) Microphotographs of the Mona Complex. 1. Schist with encarsioblast. 2. Green-mica-schist. 3. Bedded Jasper. 4. Boulder in Skerries Grits. 5. Boulder in Skerries Grits. 6. Tylry Grit. See Appendix 3.

(Plate 3) Ellipsoidal spilitic lava. Dunes of Newborough.

(Plate 4) Intersticial jasper between spilitic ellipsoids. Dunes of Newborough.

(Plate 5) Microphotographs of the Mona Complex. 1. Ellipsoidal Spilite. 2. Variolitic Spilite. 3. Glassy Variolite. 4. Albite-Diabase. 5. Jasper. 6. Spherulitic Jasper. See Appendix 3.

(Plate 6) Rose-Limestone with ellipsoidal structure. Dunes of Newborough.

(Plate 7) Autoclastic Melange. Coast near Porth Cadwaladr, Bodorgan.

(Plate 8) Siliceous Gwna Green-schist with venous quartz-augen. Ynys Gaint, Menai Strait.

(Plate 9) Microphotographs of the Mona Complex. 1. Limestone with Spilite. 2. Gwna Green-schist. 3. Gwna Basic Schist. 4. Gabbro-Schist. 5. Tremolite-Schist. 6. Actinolite-Epidosite. See Appendix 3.

(Plate 10) Microphotographs of the Mona Complex. 1. Crypto-crystalline Hornfels. 2. Mica-Hornfels. 3. Hornblende-Hornfels. 4. Epidote-Hornfels. 5. Albite-Schist. 6. Graphitic Schist. Note to 5 and 6 — A figure of typical Penmynydd mica-schist ought perhaps to have been given. But its usual, crystalline characters can be seen in these, if we disregard the porphyroblasts and encarsioblasts. See Appendix 3.

(Plate 11) Folded Penmynydd Mica-schist with quartz-augen. Graig-fawr, Holland Arms.

(Plate 12) Microphotographs of the Mona Complex. 1. Hornblende-Gneiss. 2. Sphene in Gneiss. 3. Sillimanite-Gneiss. 4. Diorite in Gneiss. 5. Sillimanite-Gneiss. See Appendix 3.

(Plate 13) Albite-pegmatite in hornblende-gneiss. Clegir-mawr, Gwalchmai.

(Plate 14) Micaceous gneiss with knots of albite-granite. Coast of the Gader Inlier at the Fox's Den.

(Plate 15) The Banded Gneisses. Henblâs, Llandrygarn.

(Plate 16) The North Stack and the sea-cliffs of the Holyhead Quartzite From the South Stack Moor. Height seen = 582 feet. Note.—The feature determined by the North Stack fault runs on, from sea-cliff, up the mountain-side, below the sky-line.

(Plate 17) The Namarch Fault. Porth Namarch.

(Plate 18) Minor isoclines in the South Stack Series. Near Porth Rhwydan, Holy Isle.

(Plate 19) Minor isoclinal folding in the New Harbour Beds. Holyhead Breakwater.

(Plate 20) Isoclinal folding with small-scale thrusting. Salt Island, Holyhead.

(Plate 21) Microphotographs of the Mona Complex. 1. Folding in Jasper. 2. Folding in Coeden Beds. 3. Minute Folding in Mica-schist. 4. Granite Pebble in the Harlech Grits. 5. Mica-schist Pebble in the Harlech Grits. See Appendix 3.

(Plate 22) Lenticular quartzites in Autoclastic Mélange, with late basic dyke. Porth Wnol.

(Plate 23) Folding of Autoclastic Melange. Menai Strait.

(Plate 24) Bedding and foliation in the South Stack Series. Seaward end of the South Stack.

(Plate 25) The Hwch lower thrust-plane. Porth-yr-hwch. Fydlyn Felsitic Tuff thrust over Gwana Green-schist.

(Plate 26) The Skerries. From near Carmel Head. 26a Careg-onen Cliffs. Mona Complex, Careg-onen Beds, Ordovician Shales, and Carboniferous Limestone [Note.—The crags in the foreground are composed of the Careg-onen Beds, ex where to 1¾ to 2 and one eigth inches from right hand edge of view) the sharp anticline of G Green-schist (Figure 194), (Figure 195) rises from under them.].

(Plate 27) Granitoid boulder from the Mona Complex in Arenig basement conglomerate. Tywyn Trewan.

(Plate 28) Microphotographs of rocks later than the Mona Complex. 1. Oolitic Ironstone. 2. Palaeozoic Felsite Dyke. 3, 4. Palaeozoic Basic Dyke. 5. Keratophyre Pebble in Red Measures. 6. Late Olivine-Dolerite Dyke. See Appendix 3.

(Plate 29) Glenkiln conglomerate resting unconformably upon the Mona Complex. Ogo Gynfor.

(Plate 30) Paleozoic dolerite dyke on the Menai shore.

(Plate 31) The Carmel Head thrust-plane at Carmel Head. Frontispiece to Vol 2.

(Plate 32) Brecciation at the Carmel Head thrust-plane. Gwaen-ydog.

(Plate 33) Silicification obliterating cleavage. Parys Mountain.

(Plate 34) Cleavage and bedding in Cornstones and Mudstones of the Old Red series. Porth-y-mor.

(Plate 35) The-Lligwy Bay Conglomerate. Careg-ddafad.

(Plate 36) Limestone conglomerate between false-bedded Sandstones. Borth-wen, Benllech.

(Plate 37) Coral-beds: Lithostrotia, with Dibunophyllum. Penrhyn Cliff, Traeth-bychan.

(Plate 38) Sandstone-pipe in Carboniferous Limestone. Foreshore, Trwyn-dwlban.

(Plate 39) Large sandstone pipe. Cliff between Castell-mawr and Trwyn-dwlban.

(Plate 40) Outlier of bedded cherts resting upon Carboniferous Limestone. Castell-mawr, Red Wharf Bay.

(Plate 41) Undercut cliff of Carboniferous Limestone. Trwyn-dinmor, Penmon.

(Plate 42) Late olivine-dolerite Dyke. Henborth, Holy Isle.

(Plate 43) Glacial strite deflected into mouth of pipe. Foreshore, Trwyn-dwlban.

(Plate 44) Glacial sands and gravels with red boulder-clay above. Lleiniog South Cliff.

(Plate 45) Transported boulder of hornblende-picrite. Near the railway, Mynydd-mwyn-mawr, Llanerchymedd.

(Plate 46) Boulder of Galloway granite. Porth-yr-ysgaw, Llaneilian.

(Plate 47) Transported block of Carboniferous Limestone. Lleiniog.

(Plate 48) Transported boulder of Penmynydd Mica-schist, with tree growing in crack. Trefarthen.

(Plate 49) Desert scenery. Dunes of Newborough.

(Plate 50) The Menaian Platform and the Bodafon monadnock. From the roadside at Mynydd-mwyn-mawr, Llanerchymedd.

(Plate 51) The Eastern Reach of the Menai Strait. From the Suspension Bridge.

(Plate 52) The Menai Strait at the submerged watershed. Looking towards the Mountain-Land of Wales. From the top of the column..

(Plate 53) The Middle Reach of the Menai Strait. From the top of the column.

(Plate 54) The Western Reach of the Menai Strait. From above Port Dinorwic.

(Plate 55) Typical scenery of the Mona Complex. Amlwch Port Moor.

(Plate 56) Rock table of Carboniferous Limestone. Near Marian-glas.

(Plate 57) Llangwyfan Church Islet at half-tide.

(Plate 58) The same. [Llangwyfan Church Islet at half-tide] From the headland.

(Plate 59) Blocks moved by the Sea. Holyhead Breakwater.

(Plate 60) Parys Mountain, the West Pit looking towards the summit. Silurian Shale, Silicified Shale, Felsite, Boulder-clay, and Spoil-banks.

Folded-plates

(Folding-Plate 1) Section along the sea-cliffs from the South Stack to Henborth. Scale 16 inches = 1 mile

(Folding-Plate 2) Section parallel to the coast at Rhoscolyn. Scale 12 inches = 1 mile. HQ = Holyhead Quartzite, SSS A South, Stack Series, MN = New Harbour Beds , Sp.t Spilitic Tuff, T Thrust.

(Folding-Plate 3) Section through Holy Isle from the North Stack to Cymyran Bay. Scale 3 inches = 1 mile HQ = Holyhead Quartzite. SSS A South, Stack Series, MN = New Harbour Beds T = Thrust. U Serpentine. E Gabbro, TrT Tre-Arddur Thrust-plane [symbol Marine Alluvium.]

(Folding-Plate 4) Section through the western region of the Mona Complex. Scale: three inches = one mile. MN = New Harbour Beds. SP = Spilitic Lavas. MS = Church Bay Tuffs. B = Ordovician. MG = Gwna Beds. BT = Bodfardden Thrust-Plane.

(Folding-Plate 5) Section through the Northern Region of the Mona Complex. Scale: Three Inches = One Mile. MG = Gwna Beds. MN= Amlwch Beds (Bodelwyn Division). WT = Wylfa Thrust-Plane. MS = Skerries Grits and Church Bay Tuffs. MH = Coeden Beds. CT= Caerau Thrust-Plane. MN = Amlwch Beds (Lynas Division). BC = Ordovician (Arenie). CHT = Carmel Head Thrust-Plane.

(Folding-Plate 6) Section through the middle region of the Mona Complex from Trefor to Glan-traeth. Scale 2 inches = 1 mile

(Folding-Plate 7) Generalized section through the Aethwy Region of the Mona Complex. Scale: Three inches = one mile

(Folding-Plate 8) Section through Mynydd Llwydiarth. Scale 3 inches = 1 mile.

(Folding-Plate 9) Section through Mynydd-y-garn. Scale 12 inches = 1 mile.

(Folding-Plate 10) Section from Carmel Head to near Rhos-y-Cryman. Scale 12 inches = 1 mile.

(Folding-Plate 11) Section across the Principal Ordovician Area from Llanol to Prys-Owen. Scale 8 inches = 1 mile.

(Folding-Plate 12) Section through the Principal Carboniferous area from the Vale of Lligwy to the mouth of the Pentraeth River. Scale 8 inches = 1 mile.

(Folding-Plate 13) The North-West corner of Anglesey. Reproduction of manuscript six-inch map.

(Folding-Plate 14) The Skerries. Reproduction of manuscript six-inch map.

(Folding-Plate 15) Llanddwyn Island. Reproduction of manuscript six-inch map.

(Folding-Plate 16) Sketch-section across Anglesey from Torllwyn to Moel-y-don.

(Folding-Plate 17) Sketch-section across Anglesey from Amlwch to Garth Ferry.