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Nyt yy teen a Ns, 2e% ernie gat nso SWusilty Oe a . aw? ost ~ we See ee ww” wife PA Ad H! eon bene | Wey, | LMA ye" ws bol ta Sore, OL | | ‘ gen ney Si . ‘ey A ht Weenie Tt ae veNy 4h ST AL ° marin ' Y 7~ & We me es ee i = 3 a dd nn Hye Ms tty tae ALERT TT ¥ See ee Y we. Am tes Wiww Sok bee ae i Sybase ¥ Al Wr mete ye a wpev GOuY TT) a tt te LP 2 » 49 ww % he a “ty = ja SS aye w way lat =) THE Da Wesedttera OF THE ge GEOLOGICAL SOCIETY OF LONDON. EDITED BY THE ASSISTANT-SECRETARY OF THE GEOLOGICAL SOCIETY. Quod si cui mortalium cordi et cure sit non tantum inventis hzrere, atque iis uti, sed ad ultenora penetrare; atque non disputando adversarium, sed opere naturam vincere; denique non belle et probabiliter opinari, sed certo et ostensive scire; tales, tanquam veri scientiarum filii, nobis (si videbitur) se adjungant. —Novum Orgunum, Prefatio. VOLUME THE PIFTY-SECOND. on I aa 1896. fi aan mitigy *% * it Gil 1930 re) ~~ oe “i Las LONDON: LONGMANS, GREEN, AND CO. PARIS: FRIED. KLINCKSIECK, 11 RUE DE LILLE; F. SAVY, 77 BOULEVARD) ST. GERMAIN. LEIPZIG: T. O. WEIGEL. SOLD ALSO AT THE APARTMENTS OF THE SOCIETY. MDCCCXCVI. Ltst OF THE OF FICHIERS OF THE GEOLOGICAL SOCIETY OF LONDON. Elected February 21st, 1896. Weyvy—e—ew™® BrestVent. Henry Hicks, M.D., F.R.S. Wice-PrestVents. Prof. T. G. Bonney, D.Se., LL.D., F.R.S. | Lieut.-General C..A. M*Mahon. R. Lydekker, Hsq., B.A., F.R.S. Secretaries. J. E. Marr, Esq., M.A., F.R.S. | J.J. H. Teall, Esq., M.A., F.R.S. PForetqnu Secretary. Sir John Evans, K.C.B.,.D.C.L., F.R.S., F.L.S. Creasurer. W. T. Blanford, LL.D., F.R.S8. COUNECIL. H. Bauerman, Esq. Rev. Edwin Hill, M.A. W. T. Blanford, LL.D., F.R:S. T. V. Holmes, Esq. Prof. T. G. Bonney, D.Sc., LL.D., F.R.S.| R. Lydekker, Esq., B.A., F.R.S. Horace T. Brown, Hsq., F.R.S. Lieut.-General C. A. M.Mahon. . Prof. W. Boyd Dawkins, M.A., F.R.S. J. E. Marr, Esq., M.A., F.R.S. Sir John Evans, K.C.B., D.C.L., F.R.S., | Prof. H. A. Miers, M.A., F.R.S. F.L.S. HK. T. Newton, Esq., F.R.S. Sir Archibald Geikie, D.Sc., LL.D., F.R.S.| F. Rutley, Esq. J. W. Gregory, D.Sc. A. Strahan, Esq., M.A. F. W. Harmer, Esq. J.J. H. Teall, Hsq., M.A., F.R.S. R. 8S. Herries, Esq., M.A. Henry Woodward, LL.D., F.R.S8. Henry Hicks, M.D., F.R.S. Assistant-Decretary, Clerk, Librartan, anv Curator. L. L. Belinfante, B.Se. Assistants in Office, Library, and Hiluseum. W. Rupert Jones. | Clyde H. Black. TABLE OF CONTENTS. Page ANDREWS, CHARLES W., Esq. On the Structure of the Plesiosauria Resour ome tC NG ie tenn Stray erteuelea « cin aonese a + 4 af * 246 ARNOLD-BemrosF, H. H., Esq. Discovery of Mammalian Remains in the old River-gravels of the Derwent, near Derby.—Part I.. 497 Aston, Miss E., and Prof. T. G. Bonney. On an Alpine Nickel- beam, Serpentine, with Pulourites 2.50.3 0... ogee le a alin A52 Batyore, F. pz Montessts DE. Seismic Phenomena in the British iraapyiter. WC lslahes / KKK, NO MOTE) 250) to apsis' sles dial die » eeteel 651 Bonney, Prof. T. G. The Serpentine, Gneissoid, and Hornblende ecus of the Lizard District.) (Plate. .sioiec se ieee = A) , and Miss E. Aston. On an Alpine Nickel-bearing Serpen- ole eM EULE PEM UELUES Ait rales is Nat ea ty he kle vlog d ¢ Ute «fon ile las 452 BucxMay, S.8., Esq., and Epwarp Witson, Esq. Dundry Hill: its Upper Portion, or the Beds marked as Interior Oolite (g 5) im the. Maps of the Geological Survey ... 2.60. 2s0600ccneees 669 Cooxz, J. H., Esq. Contributions to the Stratigraphy and Paleeon- tology of the Globigerina-limestones of the Maltese Islands. (ANUS REELS Sie octet Sais a eb ah, aD ae nL SA ae wae eae any eae nie 461 CrosFIELD, Miss M. C., and Miss E. G. Skeat. On the Geology of the Neighbourhood of Carmarthen. (Plates XXV. & XXVI.). 525 Davin, Prof. T. W. EnekwortH. Evidences of Glacial Action in Australia in Permo-Carboniferous Time. (Plate XII.) ...... 289 Dretey, R. M., Esq. Discovery of Mammalian Remains in the old River-gravels of the Derwent, near Derby.—Part IL....... 501 Exes, Miss G. L., and Miss E. M. R. Woop. On the Llandovery and Associated Rocks of Conway (North Wales) ............ 273 1V TABLE OF CONTENTS. Page FEInpEN, Col. H. W. Notes on the Glacial Geology of Arctic Europe and its Islands.—Part I. Kolguev Island. With an Appendix by Prof. TG. BONNEY cic ost ca oes « ae oe 52 5 Part II. Arctic Norway, Russian Lapland, Novaya Zemlya, and Spitsbergen. With an Appendix by Prof. T, G. Bonnzy 72 GarvineRr, C. 1, Esq., and S. H. Reynotps, Esq. The Kildare inilier.; “(Plate SX VU 2 i, oka denen ek oon ee 587 GEIKIEF, Sir ARcHIBALD. The Tertiarv B>salt-Plateaux of North- western Murope: (Plates: XV -XUX) i)... ok en 2 os 33] GREENLY, Epwarp, Esq. The Geology of the Eastern Corner of PAM S ey Ea. oss caret Sauantnc leona Gre, oun es 8 Lwin (OES , and J. Horne, Esq.. On Foliated Granites and their Rela- tions to the Crystalline Schists in Eastern Sutherland ........ 633 GreEcory, Dr.J.W. The ‘Schistes lustrés’ of Mont Jovet (Savoy). 1 Harker, ALFRED, Esq. On certain Granophyres, modified by the Incorporation of Gabbro-fragments, in Strath, Skye. (Plates PTE SS NOU Site cae Ciel, ho neha eine ts fos 2 ots Cee 320 Harmer, F. W., Esq. On the Pliocene Deposits of Holland and their Relation to the English and Belgian Crags, with a Suggestion for the Establishment of a new Zone, ‘ Amstelien,’ and some Remarks on the Geographical Conditions of the Pliocene Epoch in Northern Europe. (Plates XXXIV. & OKA DE ihe Cae Valls ecb alee oe hee an alee 748 Hicks, Dr. Henry. On the Morte Slates and Associated Beds in North Devon and West Somerset.—Part I. (Plates X.& XI.) 254 Hux, the Rev. Epwin. On Transported Boulder Clay .......... 302 Hii, Witzitam, Esq., and A. J. Juxres-BrownE, Esq. A De- limitation of the Cenomanian:—being a Comparison of the Corresponding Beds in South-western England and Western ranice. (Plate V.) . s acccsaaievaneis seua tenes ae 99 Hinpez, Dr. G. J. Description of New Fossils from the Carboni- ferous Limestone. I. On Pemmatites constipatus, sp. nov., a Lithistid Sponge. II. On Paleacis humilis, sp. nov., a new Perforate Coral, with Remarks on the Genus. III. On the Jaw-apparatus of an Annelid, Eunicites Reidie, sp. nov. (Plates: KGL i OR TIE) ss, eee RR. Ok 438 Horne, J., Esq., and EK. GREENLY, Esq. On Foliated Granites and their Relations to the Crystalline Schists in Eastern Sutherland. 633 Huu, Prof. Epwarp. Observations on the Geology of the Nile Valley, and on the Evidence of the Greater Volume of the River dea HOMME CTO Gd « waists te Nene cite meore saat inne coe a coke 308 TABLE OF CONTENTS. Vv Page Ippines, Prof. J. P. Extrusive and Intrusive Igneous Rocks as Products of Magmatic Diiterentiation. (Plate XXIX.) ...... 606 JuKxxs-Browne, A. J., Esq., and W. Hitt, Esq. A Delimitation of the Cenomauian :—being a Comparison of the Correspouding Beds in South-western England and Western France. (Plate V.) 99 Lake, Puiiip, Esq. The British Silurian Species of Acidaspis. rretecemy esr NWN i ba cA ta atin oo eee ae. dS 5's! ah oral ealtoied 235 , and S. H. Reynoxps, Esq. The Lingula-Flags and Igneous Rocks of the Neighbourhood of Dolgelly. (Plate XXIV.) .... d11 Lamp.iuen, G. W., Esq. On the Speeton Series in Yorkshire and _- . - CLOUT NE he cach rn iene Mee eee ae amr ee i79 Marr, J. E., Esq. Additional Notes on the Tarns of Lakeland .. 12 MercatFE, A. T., Esq. The Gypsum Deposits of Nottinghamshire seem Deu Dene: | CAUSETECL.)) oa chown ow sacle arse ne ane ho 0 ee 46] Pavuiow, Prof. A. P. On the Classification of the Scrata between the Kimeridgian and Aptian. (Plate XXVII.).............. 542 Prewuer, Dr. C.S.pu Ricus. Glacial Deposits, Preglacial Val- leys, and Interglacial Lake-formations in Subaipine Switzerland. 556 REED, F. R. Cowrer, Esq. The Fauna of the Keisley Limestone. Seeetimiem (de lates Nek, WAX TE Aris ie aun aup'ens eon ge ys 407 Rem, CLemMEnt, Esq. The Eocene Deposits of Dorset .......... 490 ReyNoxps, 8. H., Esq.,and Puiyip Laks, Esq. The Lingula-Flags ‘and Iyneous Rocks of the Neighbourhood of Dolgelly. (Plate “EET SCE 2 SO Neal ae 511 , and C. I. Garprner, Esq. The Kildare Inlier. (Plate ~ TEES RCTUL) 2 fae Ce tere NII OER Deh IE 587 Rur ey, Franx, Esq. On the Alteration of Certain Basic Eruptive iocks irom Brent Tor, Deyon, (Abstract) .........6c0 505% 66 SKEAT, Miss KE. G., and Miss M. C. CrosFietp. On the Geology of the Neighbourhood of Carmarthen. (Plates XXV.& XXVL.) 523 STRAHAN, A., Esq. On a Phosphatic Chalk with Holaster planus at Lewes. With an Appendix on the Foraminifera and Ostra- eMeb ye Cr AP NIAING HISQ. isl asset's ayeie 9 sels «mievavstash ® fue 463 ——., On Submerged Land-surfaces at Barry, Glamorganshire. With Notes on the Fauna and Flora. By CLEMENT REID, Esq. And an Appendix on the Microzoa. By Prof. T. R. Jonzs pate eR EOMENVAIN s HISQ Ct. arr oda as ciete a's sie ej cress os wee doe e's A474 TatmaGe, Prof. J. E. Notes concerning certain Linear Marks in perumientany Timi: CAUSE AC.) ie cade cieidss sclecseee vewees 461 Wutson, Epwarp, Esq., and S. S. Buckman, Esq. Dundry Hill: its Upper Portion, or the Beds marked as Inferior Oolite (g 5) in the Maps of the Geological Survey ........0-eseseeeees 669 V1 TABLE OF CONTENTS. Page Woop, Miss E. M. R., and Miss G. L. Erurs. On the Llandovery and Associated Rocks of Conway (North Wales) ............ 273 Woops, Henry, Esq. The Mollusca of the Chalk Rock.—Part I. Gelanes AV.) Wehia t rete cpiaciie as Ge ss c+ oe ss eee 68 Woopwarp, Dr. Henry. On some Podophthalmatous Crustacea from the Cretaceous Formation of Vancouver and Queen Char- Hobie lands thease week sek sa ak s+ 6 oss nn 221 ——. Ona Fossil Octopus (Calais Newboldi, J. de C. Shy. MS.) from the Cretaceous of the Lebanon. (Plate VI.) .......... 229 PROCEEDINGS. Proceedings of the Meotings. sui shies siete was ence > is i, Cx1x PRUMUPISBEPOFE 4. y. Sik owog curls e sits ss ebe vs os ee Vili List of ingheve BO: LAUDER: t.5 chon eee pe eiees Goes Ones en X1V List piworeion Members. sc. «as >) esos Sone Ope h +, ceehen eee XXKV lnist or Moreien Correspondents, ....-.ieceras soaene se XXV1 ieisteon AV ollaston Medallists, .......+.00 000000» 01+ ene =p XXVil Piston Murchison Medallists, «i. 000 eso «2 + >> oe XXIX asimst Muyell Medallists)’ :c\5;sc:s% ae» eee 0s outs ses pees ee kk ikiecoo: wissby Medallists ¢ oi... sauce evs aca cise er sles Roe 4.0.41 Applications of the Barlow-Jameson Fund ............0e+00e XXxl CTL MEL: ieee sh. via p inks se 4s ais w oie e-waste oe XXXli PAumeEU ROL Jee NUGO AIS, (GLE. {is i » iaje aid Bias (amg uts8)s (pcos b sleet, XXXIX Anniversary Address ..... Rate i iw Pate GR eter oh xc isk Waa Se Alo eee hi Bpecial General Meobine «2.04% e550.9 25.6 eee a oe cir 4 ok One CXX1V Dawson, Sir Witittam. On Eozoon canadense ......0...05.. CXXVIl Hicks, Dr. Hunry.. Announcement of decease of Sir Joseph THES IaNCIN 5 Siete Outlet At SII Nu a CXXVi Warts, W. W., Esq. On Specimens from the Olenellus-zone at INTIMA VON A/es0s cea Sapa CAI ae eh. g Sy oe ae vi LIST OF THE FOSSILS DESCRIBED AND FIGURED IN THIS VOLUME. [In this List, those Fossils the names of which are printed in Roman type have been previously described. ] Name of Species. | Formation. | Locality. | Page PoRIFERA. ete mee | Yoredale Beds . | Yorkshire ...... | 438 ANTHOZOA. Paleacis cuneiformis. Pl. xxiii.) { St. Louis . AEC MOND sacaescon sane sesesnane- { Group).2-522--- \ Tndiiamay <.>.2-22. 445 humilis, Pi. xxiii. figs. 1-| { Carboniferous MRE is de jsieieole vaansewe enna { Limestone ... } Stonyhunst Pals cal — obtusa. Pl. xxiii. figs. 17-| { Carboniferous RUSTE eee suis cals asiaidaduisne seid { Limestone ... | Wexford qLane) Eee TRILOBITA. Acidaspis Barrandei. PI. viii. figs.| Wenlock Lime- 1-3 : Bee sctasty sclectci(u .25E06.6 | Keisley ......... 423 Macrvra. oo cai Whiteavesii. Figs. ‘|} Caeieentas Geil | here 293 BRACHYURA. Hemolopsis Richardsom. Fig. 3... f Runes Charo 994 Paleocorystes Harveyi. Fig. 4 ...|\Cretaceous...4/)~ 225 Plagiolophus vancouverensis. Figs.| | | ee | BREE O Bese sao: sabe snmateey-teteas: J f ea al Peay ANNELIDA. Eunicites Reidie. FP. xxii. figs. 2,) Lower Carboni-| Halkin ass | OP AMAIG Sac las ntocees Rebelo ekler ferous. GBI cn nenaataed . 448 FOSSILS DESCRIBED AND FIGURED. 1X Name of Species. Formation. Locality. Page BRACHIOPODA. Crania, sp. Pl. x. figs. 9 &10 ...| ) | Mullacott ...... 270 Lingula mortensis, P1.x. figs. 1-5. 266 Orthis rustica, Pl. xi. figs. 7-10... } North Devon . { 268 Rhynchonella Lewisii (?). Pl. xi. Bog, Tol Se aed eer ete ie Barricane ...... 268 Stricklandi(?). Pl. xi. fig. 11.) } Morte Slates .{| Mullacott ...... 268 ia Hamlingii. Pl. xi. figs. Me ee ere lita aacinodsleastetau Barricane ......| 268 Pe naniisia lirata. Fig. 3 & pl. MR OO ro. ns ciste canoes suie L Ilfracombe ...... 266 sp. Pl) xi. figs. 12&13...... baes Mullacott ...... 270 LAMELLIBRANCHIATA, Aucella Keyserlingi. Pl. xxvii. JNES5 3) Cra AR Ae a Tealby Series...) Claxby..... ye. 560 volgensis. Pl. xxvii-figs. la—c.| | 549 3 , var. radiata. BL XXVii. ee eueels | onsiogton we eS 255) Ber ee Saat iF 550 Waieuia, sp. Pl. xi. fig. 18 ...:..... \ (le ebarricationvere.cc 269 Cardiola interrupta (?). Pl. xi. fig.| | | RE ae scthdvobadessieanneenn< Mullacott ...... 270 Modiolopsis barricanensis. Pl, xi.| + Morte Slates . + BIO NOM or ciscicc cise scene csi net | North Devon ...| 269 Pteringa mortensis, Pl. xi. figs. PESTS Ii cst eBbesaiphto tab 5. paoaioiren' sk ) (|. -Mullacott ...... 269 GASTEROPODA. Avellana, sp. ef. Humboldti.’ Pl. \ ( PRUE UO loc os cninicnsidodeine cpaee xt 93 Cerithiwm cuckhamsliense. P. iv. | HUMMER Osi ceicais i oeicisnenalsedeccns sive 92 Saundersi. Pl. iv. fig. 12 ... | 92 Lampusia (?) sp. Pl. iv. figs, 13 | OTA CLEC DBD Re ee 93 Pleurotomaria (Leptomaria) per- | spectiva. Pl. iii. figs. 13, 14, & \ Chalk Rock...... Warlous)...-.bs.2: 4 PES Md oe doce tbe caves veces | 86 Trochus berocscirense. Pl. iv. figs. IM 2c e Sees nies einen cos oes 88 — Schliitert. PI. iii. figs. 11 & | | iccAvctonscoe CEA nee ee 88 Turbo Geinitzi. PI. iv. figs. 5-8... 88 gemmatus. PI. iv. figs. 9 & LUNES otic cea ) L 89 x FOSSILS DESCRIBED AND FIGURED. Name of Species. Formation. | Locality. | Page SCAPHOPODA. DET ETL Ghali Rock......| Various «om | 96 CEPHALOPODA. Ammonoidea. Ammonites (Acanthoceras) hippo-| | f castanum, var. compressus. Pl. v.| | | A ia een tne Se cice cS uin aie din ‘ Cenomanian..{ | Devon............ 157 — (—) pentagonus. Pl. v.| | | ' HIS MOC IE Se wcinayee cane nce <2 cee) sinc J || Lyme Regis...... 156 Baculites bohemicus. Pl. ii. figs.) | ( RCM Oe ch Ree reels tecnica odisiein ee sie 76 Crioceras ellipticum. PI. iii. figs. UD rect tena eke bounce cecnaten ve 84 Heteroceras Reussianum. Pl. ii.| | | AUS Gee ae eee «Accu sa bates ensies . | 94 PHL dis eed S |. tou \ Chalk Rock...... Various ..:ceeeee 1 75 Prionocyclus Neptuni. PI. ii. fig. A Gcedel. cies Ar v7 Ptychoceras Smith. Pl. ii. figs. 1) | : Ri Ree cian Decaiies Ahir be ctacbeccen + | “4 Scaphites Geinitzi. Pl. iii. figs. 57,| J | 81 Octopoda. Calais Newboldi. PI. vi. ...........- | Cretaceous ...... | Lebanon.......... | 229 Teuthide. Plesioteuthis Fraasii. Fig. ......... | Cretaceous ...... | Webanon . eee | 283 PLESIOSAURIA. Plesiosaurus dolichodeirus. Fig. 1 ? ? 248 macrocephalus. Pl. ix....... MAG aceon ore so-...| Lyme Regis...... 246 EXPLANATION OF THE PLATES. SKULL OF PLESIOSAURUS MACROCEPHALUS, Buckland, to illus- trate Mr. C. W. Andrews’s paper on the Structure of the PE FERTOSAPIAE OMe ee eens cise rete cet sanemechitaneecens 246 IX. PLATE PacE Microscopic sections of Banpep SERPENTINE and PARTIALLY Ue MELTED HoRNBLENDE-SCHIST, to illustrate Prof. T. G. Bonney’s paper on those rocks in the Lizard district ...... 17 IL-IV CuaLk Rock Mo.uuvsca, to illustrate Mr. Henry Woods's re Papers Oy HOSE LOssIIS) oo pinta coeaganes sia serirelndaisgeh jones desees 68 CENOMANIAN Ammonites, to illustrate Messrs. A. J. Jukes- Vv. Browne and W. Hill’s paper on the Stratigraphy and Palx- Ontology OF that TORMIA GION 6) aonsamce ca adaeneeqosaneesedeeese aa 99 VI Catais NewBo1piI, to illustrate Dr. Henry Woodward’s paper ; OUR CNA MOSS eta tnainfo'eictocsingseaspiajcigan dicina sieeaisain aisieddeeoaeae es 229 VII. & f Brrriso Acipaspis, to illustrate Mr. Philip Lake’s paper on VIII. the British Silurian Species of that genus ..................+6- 235 Pauzozoric Mouuvusca or Nortu Devon, to illustrate Dr. Henry Hicks’s paper on the Morte Slates and Associated Beds in North Devon and West Somerset ..............0e0000: 254 X. & XI. NIFEROUS GLACIAL Breps At Baccuus Marsa, to illustrate Prof. T. W. Edgeworth David’s paper on Evidences of Glacial Action in Australia in Permo-Carboniferous time. 289 Microscopie sections of GRANoPHYRES wiTH Forztcn Incuv- stons, to illustrate Mr. Alfred Harker'’s paper on those rocks, modified by the Incorporation of Gabbro-fragments, in Strath GSisye)) et is ser Pie eter suited ciselclavins a docGondensesews 320 XIII. wn. See AND VERTICAL SECTIONS OF THE PERMO-CARBO- XIV. | { Voucanic Neck at Stromo (Faur0z); PART oF VOLCANIC Necs, Canna; Dtn Mor, Sanpay; Don Brag, SANDAY, XV_-XIX.4 seen FROM THE SOUTH-WEST and seen FROM THE NorTH, to illustrate Sir Archibald Geikie’s paper on the Tertiary \ Basalt-plateaux of North-western Hurope.................006 331 XX. & { Trrnoprres rrow THE KeisLey Limestons, to illustrate Mr. F. XXI. | R. Cowper Reed’s paper on the Fauna of that horizon ... 407 xii EXPLANATION OF THE PLATES. PLATE PAGE PEMMATITES CONSTIPATUS, Sp. nov., and XXII. EKunicites REIDIz, sp. noy.; and XXIII. { Pauzacts, to illustrate Dr. G. J. Hinde’s paper on those = L SOIT Esau AA SRR Gros ka At a EE GrotocicAL Map or tae Nerigusournoop or DoLGELLy, XXIV to illustrate Messrs. P. Lake and 8. H. Reynolds's : paper on the Lingula-Flags and Igneous Rocks of that : DISORICE | ooccywicnepencomeecateasnckdensecess-se0so0esssacr 511 XXV ( GroLocicAL SKETCH-MAP OF THE NEIGHBOURHOOD OF a ak MARTHEN ; and CARMARTHEN TRILOBITES, to illustrate Miss M. C. Crosfield 7528 XXVI. and Miss E. G. Skeat’s paper on the Geology of that | GUBEGICLS eam ee ser tcc erences cn seascebcnnesmnueinener ios eaneee J AUCELLA VOLGENSIS AND AUCELLA KEYSERLINGI, to illustrate XXVII. Prof. A. P. Pavlow’s paper on the Classification of the Strata between the Kimeridgian and the Aptian............ 542 Microscopic sections of LavAs AnD ASHES FROM THE KILDARE XXVIII. InuteR, to illustrate Messrs. 8. H. Reynolds and C, I. Gardiner’s paper on the above-mentioned Inlier ............ 587 ‘GEOLOGICAL SKETCH-MAP OF PORTIONS OF IpAno, Montana, AND WyominG, showing in part the Distribution of the XXIX.{ Volcanic Rocks, to illustrate Prof. J. P. Iddings’s paper on | Hxtrusive and Intrusive Igneous Rocks as Products of \OP Mag mintie WimeremblatlOn ...-..0 0.00.00. ences. e+e coder eeeeeeee 606 SeismicaL Maps or THE Britisu Istes, tHE Inp‘An EMpiRe, XXX.-— AFRICA, AND THE Lesser ANTILLES, to illustrate M. F. de XXXIII. Montessus de Ballore’s paper on Seismic Phenomena in Ge SUIS MAURO Soe cate mete celine) ob psieineikie nincinjee + wei Ee 651 Grotocican Mars or NortH-western Europe and the Crag XXXIV. & District oF SuFFOLK AND Norro.k, to illustrate Mr. F. XXXY. W. Harmer’s paper on the Pliocene Deposits of Holland, (EL eet OS ic. eho, Le A ORE 748 PROCESS-BLOCKS AND OTHER ILLUSTRATIVE FIGURES BESIDES THOSE IN THE PLATES. FIG. PAGE 1. Sketch-map of the north-western quadrant of Mont Jovet...... 5 9 Sketch of Dolomite-outlier at the foot of the western end of WOE rt Gest A EMEA a aeaies Osis den ctcte cenafan ate sabe anidh tcsssrkaes 7 fee section near Watendlath: Varn io .oncedennasecesenuvenadss0nsacveee 13 Dome echion across Hard Warn 5.22.5 ).h ane-cctnascidcce< dana idecdsda.cece 14 ome eatte Onder e Wael odin te ac sacanietcuiravcauwiagaysteeasaicarsan cheviehends Se 14 1, { One of four ‘ eyes’ in hornblende-schist, north of Porthoustock . : IME wanton sono jsut at Moca= «sloadueduidccamdeanyiakacnaesapeadesscuesecases, 19 Pam VerGh NOmABleMGtte, COA. oa. ducmcacaae napa t see encensks ddan sabe adhoc 20 3. Granulite included in serpentine, east of the Lion Rock......... 27 4 Serpentine adhering to a ‘step’ of granulite, in Polbarrow ; eee ck eet cats eae cutchss ce nlsng Seca sists vemenneriiessedeslactes 29 5. Banded granulite, south of Poltesco Cove ...............ceeceeseeees 29 6, 7. Serpentine and banded granulite, Enys Head ..................... 30 8. Do. Do... Polbarrow Cove) «.....5..:.. 30 9. Banded hornblende-schist in serpentine, Potstone Point......... 32 Intercalation of serpentine and hornblende-schist, gully north 10. ‘ PUL CIRC DI as Pe Re = Se ne eee 30 Gabbro included in granular dolerite, south of Porthoustock Le aA RS eR tee eet ecl sbi toes nee Sac ceuichele sac tceanbomctncecleveeecsens 43 Diagram showing the expansion of the Cenomanian of Devon at Beer Head and Hooken Chiff X1V PROCESS-BLOCKS AND OTHER ILLUSTRATIVE FIGURES. FIG. PAGE Tabular view of South-coast Sections ..............-2-00 facing 114 Section of the cliffs at La Héve, below the Cenomanian ......... 119 Sections of the Cenomanian at Brunval, St. Jouin, and La MG VG 9 od ee cnhaseecaven-aoscisceeatiner esol Reuutcasscees saneasis facing 124 Comparison of English'and French Sections ............ facing 172 Sketch-map of the Yorkshire and Lincolnshire Wolds Diagram showing the Correlation of the Speeton Series in Workehire and Dincolmehire els. se ls.t 6 aces thes cesevee facing 212 aoa) Calhanassa WIMLEGUESIT, BD: NOV: cc 0c. nea sneoe+s vsannces eee 223 3: Aomolopsts Titehasgsont, 8. Ove 4 sis. .ee bec sleds -/0: .. WANN, retires th ethe cic, ede oe siete Oo a aaa 2 11-25 } 5 PR TREIE See taneaneen saat Zaccagna, op. vit. (1892) p. 397, & pl. v. sect. 2. B2 4 DR. J. W. GREGORY ON THE ‘ SCHISTES [Feb. 1896, laid down later, and upon the others. In fact, what according to Zaccagna is the oldest rock in the mountain, according to Bertrand is the newest. The differences, moreover, are as important as they are absolute. According to Bertrand, the ‘ schistes lustrés’ pass laterally into the Trias (see op. cit. fig. 2, p. 128, and fig. 9, p. 135). According to Kilian the presence of the ‘ schistes lustrés’ seems to exclude the presence of the Carboniferous, and he therefore suggests that the ‘schistes ’ may be Carboniferous; though he admits that this cannot be definitely determined. If, however, Zaccagna and Lory be correct, and the central rocks of Mont Jovet are ‘schistes lustrés, then these occur surrounded by both Carboniferous and Triassic rocks. In that case, it cannot be maintained that the ‘ schistes lustrés’ are the eastern metamorphosed condition of the beds which farther west have remained as non-foliated sediments. The identification of any ‘ schistes lustrés’ in Mont Jovet would therefore alone be fatal to the view that these rocks are Carboni- ferous or post-Carboniferous in age. Having failed on previous occasions to obtain definite proofs of the pre-Carboniferous age of the ‘schistes lustrés’ in the Cottian Alps, I was the more im- pressed by Bertrand’s reversion to Lory’s theory. The perusal of Bertrand’s paper did not carry conviction ; but respect for the care and ingenuity with which the author had solved the puzzling problems of Provencal geology necessitated the careful consideration of his views. I therefore resolved to visit Mont Jovet as soon as the melting of the snow rendered geological work possible, and exa- ' mine the mountain independently in order to see whether it does contain any ‘ schistes lustrés’; and, if so, to try to construct a more detailed geological map than has yet been published... So much, however, of the mountain is covered by pine-forest and talus, by moraine and meadow, and so many of the important junction-lines are thus hidden, that it was impossible to make a geological map sufficiently complete to repay the time which it would occupy. I had therefore to be content with a sketch-map based on the French Ordnance survey on the scale of 1: 80,000} Standing on the hills on the northern side of the Isére, at any good point of view between Moutiers and Aime, the southern side of the valley is seen to consist of three main divisions. The lowest part is formed of steep cliffs of dark-coloured rocks, covered by vineyards, meadows, and woods. Above this is a belt of pine-forest ; in this occur at intervals cliffs of buff dolomite and white gypsum, and occasional crags and pinnacles of the former rock. Above this belt are the high-level pastures, formed of undulating meadow-land passing up into irregular rock-strewn slopes, and a group of peaks, of which the highest is Mont Jovet. Further examination of this mountain-mass shows that these three zones are each formed by different series of deposits. The lower slopes are occupied by Car- 1 Albertville, S.E. feuille 169 dis, type 1889, Vol. 52.| LUSTRES ’ OF MONT JOVET (SAVOY). 5 boniferous; the cliffs above by Triassic dolomites and gypsums; the highest meadows and the central peaks by the rocks whose age is in dispute. The area more especially examined was the north-western quadrant of the mountain, which is included in the sketch-map, fig. 1. Fig. 1.—Sketch-map of the north-western quadrant of Mont Jovet. rE Longefoy 344 a 8 . ties Eee ; EH i ae / as : EEE : inte : EEEH an rH 7 H FEE nee ; Sika 58a GS : an a ; y [M Uiguggyenio Gy iim cr ~ ir ~ 'y ¥ | rr Ve Sa innae = Hy Hoe SNH e A ia RU ane 4 1 Zinn oH NY AM! bese L fa ESS Al tet ena tt ct ce} pan Uy s (ane. am q oe at cry i) iene) ha 3 r Ct ine ct aoa ma “ vee A EERE EEEEEE ES EERE AN noe oe sealer suscasascea/a woe! rt ros ' s] =" on ct He a Perr Y,\ her Pro oy Preoce co Nt A coo cece a = Y rt Sune | t 6 EEE (Ti * rt z > Py aa zy as oH Ptr é tes cr Poet Y \ejsne oo eros A% S { rr Be Pog ari erate “IQ anne Cons S ~a--— Footpaths | Heights in metres. » ede | Zar rias. EEE Carboniferous. = pentine, fs sees praghivzestone Fen] Overtzttes &c Lustrés. in Schistes in Schistes | Lustrés, Lustres. as: Dee : F Seale : 30,000 792 inch to the mile. The Carboniferous rocks are of the ordinary type of this series in the Tarentaise ; good sections and exposures can be seen on the banks of the Isere, and around the hamlets of Hauteville and Notre Dame du Pré, at the height of 2500 feet above the floor of the valley. The superposition of the Triassic rocks to these can be clearly seen around the latter village, for the Carboniferous beds there form a platform upon which the Triassic limestones rest. It is unnecessary to give any description of the characters of the Carboniferous and Triassic rocks, but those of the third series require more careful notice. For the question as to whether or no these are part of the ‘ schistes lustrés’ can be determined by litho- logical evidence alone. The rocks in question consist of three main types: 1st. A series 6 THE ‘ SCHISTES LUSTRES’ OF MONT JOVET (SAVOY). [Feb. 1896. of limestones sometimes massive, sometimes passing into calc-schists, the beds of which are separated by beds of crushed phyllites ; 2nd, gritty quartzites and irregular quartzitic schists; and 3rd, talcose lustrous schists. These three sets of rocks occupy the whole of the central part of the mountain, including the summit of Mont Jovet and the four subordinate peaks, namely, the Grande Cote (2543 metres), La Cote (2058 m.), Mont des Arrhets (2440 m. and 2492 m.), and the ridge including the 2272 and 2370 metre-points north of Mont Jovet, between the upper valleys of Nant de Thionet and the Vallon des Frasses. The main problem is the relation of this group of rocks to the Trias upon its margin. The position of the junction of the Triassic limestones and the ike of this central series, or, as we may at once, for convenience, call them, the ‘schist series,’ can be easily determined to within a few yards. The actual junctions, however, are hidden. I did not, in fact, find a single case where, in a clear cliff-section, the actual superposition of the two could be seen. In several points, as at the junction of the gypsum and the schists in the hollow between the 2067 metre-point and the western end of the Mont des Arrhets, it certainly appears as if the Trias underlay the schists; for the apparent dip in the gypsum is to the south-east, and under the schists, Itis not, however, certain that this bedding in the gypsum is true stratification ; but even if this be so, the apparent super- position can be explained as due to an overfold, or to the subsidence of the limestones, owing to the solution of the gypsum along lines of drainage. The latter cause has certainly rendered the apparent dip in the gypsiferous beds very unreliable. The most instructive case illustrating the relation of the two series was found a little to the north-west of the western end of the Mont des Arrhets. There occurs a hummock of the gypsiferous part of the Trias, marked on the map as the 2067 metre-point. The stratigraphical relations of this mass are clear, for the junction between it and the schists can be traced all round, excepting for a few yards on the north-eastern side. The evidence is sufficient to show that this hillock is simply a mass of the Trias, left as an out- lier on the flanks of a slope of schists. The relations of this Trias are illustrated by the accompanying sketch (fig. 2). ‘The fir-covered boss in the centre is the 2067 m. point; the lower knoll to the left (the 1894 m. point) is the upper termination of the main outcrop of the Trias. On the extreme right is a low cliff of schist, which is part of the western end of the Mont des Arrhets. The schists can also be seen in some low crags on the eastern side of the valley, to the right of the 1894 m. hill. They can moreover be traced over the whole of the grassy slope from the end of the Mont des Arrhets, round the southern side of the 2067 metre-boss, to the valley to the west, and thence up the lower part of the slope of the 1894 m. point. Fortunately, the ground on the southern side of the 2067 m. point is moutonnée, and the crests of the ridges either just reach the surface, or can be exposed with but little trouble. It is thus possible to prove that the schists Fig. 2.—Sketch of Dolomite-outlier at the foot of the western end of Mont des Arrhets (seen from the cow-chalets of Notre Dame du Pré, looking northward), Valley of Mont W. end of Mont 1894 metres. the Isere. Blane, 2057 metres. des Arrhets. Trias, Schistes lustrés, Hummocek of Trias Schistes lustrés. (schists in fore- ground), 8 DR. J. W. GREGORY ON THE ‘ SCHISTES [ Feb. 1896, are continuous from the end of the Mont des Arrhets, round the Trias outlier, to the crags in the valley below, where they finally plunge under the main sheet of Trias. On the northern side of this boss of dolomite there is a very steep slope down to the Nant de Thionet. The upper part of this slope is masked by pine-wood and talus, and outcrops of rock im situ are very scarce. The complete isolation of the limestone-boss cannot therefore be proved. The general characters of the cliff to the north leave no doubt in my mind that it is wholly formed of schists; all the exposures seen were of rocks of this series, and these were sufficiently numerous to restrict the possible connexions between the dolomite of the boss and that of the cliffs below to a very narrow band. This band would run almost at right angles to the strike of the schists, and thus can only have been formed by deposition upon these. Its existence, therefore, would strengthen the evidence in favour of the view that this dolomite is an outlier from the limestones below, from which it has been separated by denudation. In this case the sheet of limestone of which it was once a part must have been deposited on the flanks of the old schist series. A second line of enquiry is as to the occurrence of fragments of one formation in the other. It is natural to turn to this for assist- ance, for one definite case would settle the question. In the schist series there are some crushed grits which must formerly have been . fine pebble-beds. I searched in these in vain for any fragments of the dolomite. In the Trias there are bands of conglomerate, crowded with included fragments, ‘The first of those examined was at the Chalets du Préjordan; a small pit there yielded numerous fragments of what appeared to be altered dolomitized specimens of the limestones in the central schist series. I could not, however, there find any unquestionable specimens of the ‘schistes lustrés’ themselves. At a point near Notre Dame du Pré more satisfactory evidence was obtained. The Triassic dolomites there contain some beds of pebbles, many of which appear to me to be unquestionable fragments of the ‘ schistes lustrés.’ Some of these included frag- ments may be matched exactly in the cliff of schists, just above the bank of limestone in which the fragments occur. A third line of argument may be based on the unaltered condition of the Triassic rocks in contrast with those of the central schist series, The Triassic dolomites show no sign whatever of foliation. Bertrand has remarked the intensity of the puckering and folding of the rocks of the centre of the massif, and admits that this is not easy of ex- planation. Lory had previously recorded the occurrence of albite- crystals in the limestones of the schist series, but regarded this as only an illustration of the extent to which the Triassic rocks have undergone alteration. If the metamorphism of the schists were most strongly marked in the centre of the massif, and least so on the margin, it might be explained as due to post-Triassic movements. But this is not the case. The extent to which the rocks have been rendered schistose depends on the character of the rocks and not on their position. Some of the rocks in which the foliation is most marked occur on the margin of the series within 10 yards of the dolomite. Vol. 52.) | LUSTRES ’ OF MONT JOVET (SAVOY). 9 On the other hand, the member of the schist series which at first sight appears least altered is the massive limestone of the Grande Cote, nearly in the centre. Even between the least altered of the limestones of the schist series and the Triassic dolomite there is a great difference. Microscopic examination shows that the latter is a normal dolomite, and does not contain any authigenous crystals of albite. The limestones of the schist series, on the other hand, are really calciphyres, show traces of intense crumpling, and con- tain abundant crystals of plagioclase and epidote. If the schists be really younger than the Trias, it appears inexplicable why these should have been so intensely altered, while the dolomites in contact with them should have escaped. It is therefore contended that the evidence is conclusive that the Triassic dolomites have been deposited unconformably on the edges of an older series of schists. It remains now to consider what evidence is available to determine with which member of the schist series in the Western Alps these must be correlated. ‘The contorted, lustrous, black, talecose schists which occur on the summit of Mont Jovet remind one at once of the ‘schistes lustrés’ of the classical area around Cesana, z. ¢. of the ‘ Kalkschiefer’ of Diener, the ‘Calcescisti’ of the Italian geologists, or the ‘Upper Archzean schists’ of Prof. Bonney. Zaccagna—whose acquaintance with these schists is intimate—has no hesitation in regarding these as part of this series. Lory, who knew both series extremely well, also unhesitatingly identified the Mont Jovet rocks as ‘schistes lustrés.’ It must be admitted that in one respect these rocks are not typical representatives of the ‘ schistes lustrés’ series, and that is the great development of massive limestones and quartzitic beds. Bands of the same character as these occur in the ‘ schistes lustrés ’ around Cesana; but both the limestones and grits are there represented by very thin layers and films, and the main mass of the formation consists of black lustrous schists. It is these massive limestones which Bertrand has assigned to the Lias, and macroscopic examination of a specimen does not show anything fatal to this view. Microscopic study, however, reveals the fact that the rocks are entirely crystalline, and have undergone intense alteration. Sections of specimens from a boss in the upper part of the valley of the Nant Gelé, on the northern slope of the Grande Cote, and from the summit of this peak, show that. they consist in the main of crystalline, polysynthetically twinned calcite. A black carbonaceous dust occurs in irregularly crumpled and broken lines through the rock. Some small grains of plagioclase (deter- mined by Lory as albite) are scattered in the calcite at irregular intervals. Grains of epidote are fairly numerous. The rock is therefore a calciphyre, and is very different in structure from the Jurassic limestones of the neighbourhood. ' The black lustrous schists, with which these limestones are seen to be interstratified both on the central peak of Mont Jovet and on the flanks of the Grande Cote, are, however, thoroughly typical 10 DR. J. W. GREGORY ON THE ‘ SCHISTES [Feb. 1895, ‘schistes lustrés.’ A specimen collected on the western aréte of Mont Jovet, just below the summit, agrees in its microscopic struc- ture with the schists of the Cesana district. The microscope shows that it consists of alternate layers of a black, indeterminate, and a clear crystalline material. The rock is intensely crumpled, and the black bands often thin out along lines of shear. A quarter-inch objective resolves the black material into a very fine calcareous and argillaceous dust, and the white clear layers into a mosaic of quartz in which occur tiny crystals of white mica. There is no sign of calcite in the rock, nor does it effervesce with acid. ‘The rock, therefore, agrees exactly with one of the finer and non- calcareous varieties of the ‘schistes lustrés’ of the Cottians.* It appears to have been originally a fine-grained mudstone. It may be suggested that possibly the ‘schistes lustrés’ and the limestones are not part of the same series. But that they are so is very clearly shown just below the summit of Mont Jovet. A few yards along the ridge to the east a layer of limestone strikes right across the ridge. Some rocky ribs run down the northern face at this point, and in one of these, about 30 yards east of the summit, the junction can be clearly seen. It could not be traced far, as there was too much snow on this face of the mountain at the time of my visit; but the exposures were sufficient to demonstrate the interstratification of the limestones and the schists. In spite, therefore, of the unusually extensive development in the schist series of this massive non-foliated limestone, I feel bound to admit that Lory and Zaccagna were right in identifying the central rocks of Mont Jovet as ‘ schistes lustrés.’ There is nothing at all improbable in the outcrop of these schists in Mont Jovet, if they be pre-Carboniferous in age. This series is extensively developed 15 miles to the east and 20 miles to the south, and its extension thence westward bclow the Carboniferous and Trias rocks, as suggested in Zaccagna’s section,” is not in any way improbable. Another feature which allies the rocks of Mont Jovet to the erystalline schist series, is the occurrence in them of basic igneous rocks of the ‘pietre verdi’ type. These have been recorded on the mountain by Favre, as well as by Zaccagna and Bertrand. A mass of serpentine occurs in the schists in the upper part of the Vallon des Frasses: it appears almost identical with that described by Bonney from the pass of Mont Genévre, which has been: proved to be pre-Triassic.* I should be loth to use the characters of intrusive igneous rocks as a proof of age, but the coincidence in this case is significant. 1 It may be compared with Prof. Bonney's description of the microscopic structure of the ‘schistes lustrés’ near Cesana, Quart. Journ. Geol. Soe. vol. xlv. (1889) p. 103. ‘ 2 Zaccagna, ‘ Riassunto Osserv. Geol. Alpi Graie,’ Boll. R. Com. geol. Ital. vol. xxiii. (1892) pl. v. sect. 2. 3 'T. G. Bonney, ‘Two Traverses, etc., Quart. Journ. Geol. Soc. vol. xlv. (1889) p. 80; Cole and Gregory, ‘ Variolitic Rocks of Mont Genévre,’ 2bzd. vol. xlvi. (1890) p. 805; Davies and Gregory, ‘ Geol. Monte Chaberton,’ zbid. yol. 1. (1894) p. 307. Vol. 52.] _ LUSTRES’ OF MONT JOVET (SAVOY)... 11 CoNCLUSIONS. It is contended, on the evidence above cited, that Lory and Zaccagna were right in identifying the central rocks of Mont Jovet as ‘ schistes lustrés, for this conclusion is supported by their lithological cha-- racters and the nature of the igneous rocks associated with them, and is not opposed to their stratigraphical relations. It is further shown that the schists in question are older than the Trias (1) by the occurrence of fragments of the schists in the Trias; (2) by the discordance of strike between the two series; (3) by the occurrence of masses of dolomite resting unconformably on the flanks of the schists; and (4) by the fact. that the Trias has escaped the metamorphism which the schists have undergone. The probabilities are all in favour of the schists occupying the same relation to the Carboniferous as they do to the Trias; while the close approximation of the schists to the former show that the schists are not the altered representatives of the Carboniferous, We must therefore conclude that the ‘schistes lustrés’ are pre- Carboniferous, but evidence by which finally to assign them to any exact horizon before this date is still wanting. Discussion, Prof. Bonnry expressed his sense of the great value of Dr. Gregory’s paper, which he regretted had been pushed into a corner by the time which he had been obliged to take up for his own. From his general knowledge of the district and intimate acquaintance with other parts of the Alps, he had no doubt that Dr. Gregory was quite right in his interpretation, and that the crystalline schists, often called the ‘ schistes lustrés,’ were certainly pre-Carboniferous, and probably much older. Dr. Du Ricue Pretier fully agreed with Prof. Bonney’s remarks as to the great importance of the subject dealt with in the paper, and was gratified to see that the Author substantially endorsed the views of Zaccagna, who had done so much excellent work in the Western Alps from 1887 to 1889, and, by extending the survey on the Italian side for fully 30 miles into the Vanoise district in Savoy, as far as the valley of the Isére, had conclusively shown that Lory’s views as to the Upper Triassic age of the calcareous schists, or ‘ schistes lustrés,’ were utterly untenable, and, further, that the bulk of the mica-schists referred to by Termier as Permian are also, like the ‘schistes lustrés,’ pre-Carboniferous—indeed, of Archean age. The speaker had visited the Savoy district some years ago, and, in his opinion, the occurrence in the central mass of Mont Jovet of serpentine, gabbro, and so-called green Alpine marble (as quarried near the summit), under conditions strictly analogous to those on the Italian side near Susa, and also in Liguria, affords a strong’ argument in favour of the Savoy ‘schistes lustrés’ being, like those of the Italian localities, of Archean age. The AvurHor replied, thanking the Fellows for their reception of his paper. 12 MR. J. E, MARR ON THE TARNS OF LAKELAND. [Feb. 1896, 2. Avprtronat Notss on the Tarns of Laxetanp. By J. E. Marr, Esq., M.A., F.R.S., Sec.G.8. (Read November 20th, 1895.) Tue following notes form a supplement to a paper on ‘ The Tarns of Lakeland’ read before the Society in 1894. I have had the opportunity during the present summer of devoting more time to the study of Watendlath Tarn, and have examined three other tarns of some interest. (a) Watendlath Tarn. In my former paper, I stated that in the case of Watendlath Tarn ‘a great mass of drift is plastered against the east side of the valley, and may have filled the old valley. I. have since ascer- tained that there is no old valley there, but that the solid rock runs -all round the northern, eastern, and southern ends of the tarn: I furthermore stated that ‘on mounting some way above the tarn I saw indications of the possible existence of a moraine-filled depression’ on the western side. J have now examined this de- pression and satisfied myself that beneath it lies buried the old valley, the stream from which ran down into Borrowdale near Ros- thwaite—that is, about 3 miles south of the present junction of the Watendlath valley with Rosthwaite, near Lowdore. ‘This moraine- filled depression runs close to the path from Rosthwaite to Watendlath Tarn. The watershed here is about 200 feet above the surface of the tarn, and, as the tarn is 46 feet deep, it requires a barrier of drift over 250 feet in thickness to account for the tarn; but, as the valley is evidently a narrow one, and its course lay at right angles to the direction of the ice, the occurrence of this somewhat thick mass of drift presents no difficulty, and a much thicker mass has been recorded in the neighbourhood filling up an old valley, as proved by boring in Furness. Proceeding from Rosthwaite towards the tarn, the path ascends by the side of a stream running from Brund Fell to a spot called Birkett’s Leap, where it leaves the main stream and is carried parallel with a tributary descending from the lowest part of the watershed. The stream from Brund Fell and the lower part of the tributary stream have cut to a considerable depth between rock and drift, the northern bank of the stream being composed of rock, and the southern side of drift, so that the streams appear to be gradually cutting out the old valley (see fig. 1). To the east of Birkett’s Leap, * Quart. Journ. Geol. Soe. vol. li. (1895) p. 35. In this paper the following errata occur :— Page 39, last line, for ‘ Ask’ read ‘ Ark.’ , 42, line 7 from bottom, for ‘lower’ read ‘southern.’ » 42, line 8 from bottom, for ‘ upper’ read ‘ northern,’ » 44, line 7 from top, for ‘ east’ read ‘ west.’ », 40, line 5 from bottom, for ‘ east’ read ‘ west.’ Vol. 52.] MR. J. E. MARR ON THE TARNS OF LAKELAND. 13 the tributary crosses to the southern side of the drift-filled depression, and east of this the rock lies on the southern, the drift on the northern bank. At the top of the pass, the path is on the northern border of the drift-filled depression, which is readily traceable towards the tarn. Some way below the top of the pass on the Watendlath side, a stream called Bowdergate Gill runs along the depression, and has cut a ravine in it, which is well wooded towards the tarn. In some places this ravine is about 50 feet deep, and is cut Fig. 1. entirely through drift, w. with drift forming the bed of the stream. It may be noted that ZY on looking towards the gw eastern side of Borrow- “ig dale from below Ros- thwaite, the col above- mentioned is the only place where solid rock is . not visible against the Rea: Else sky-line for a distance of about 2 miles, and it is also the lowest portion of the sky-line in this space. There are indications of an old terrace some way above the present surface of the tarn, which are most clearly seen on the eastern and southern sides. This probably marks the original height of the old col between the former Watendlath and Lowdore valleys, which would form the exit of the lake after the stoppage of the narrow Watendlath-Rosthwaite gorge, the rocky ravine just below the tarn having since been deepened to the extent indicated by the difference of level between the present surface of the tarn and the summit of the old terrace. Stream From Brund Fell ‘ ; et (6) Hard Tarn, Helvellyn. In his paper on ‘The Glaciation of the Southern Part: of the Lake-District and the Glacial Origin of the Lake Basins of Cumber- land and Westmoreland,’’ Clifton Ward remarks (p. 161) :—‘ Just below and south of Nethermost Pike, Helvellyn, in Ruthwaite Cove, is Hard Tarn, 150 feet by less than 100 in size; it is very shallow, so that one can see the rocky nature of its bed and sides, and mark how the ice-scratches pass beneath the water from one side to the other.’ Owing to the above statement and to the small size of the tarn, which might well be a rock-basin, even if the other tarns of the district are only drift-dammed, I was particularly anxious to see this lakelet, but was prevented by bad weather in former years. This year I had an opportunity of examining it. The pond lies on a dip-slope of some ash-beds having a gentle inclination towards a steep escarpment-cliff above, which is surmounted by another dip- ? Quart, Journ. Geol. Soc. vol. xxxi. (1875) p. 152, 14 MR. J. E. MARR ON THE TARNS OF LAKELAND. [ Feb. 1896, slope; this at one time evidently contained a lakelet similar to that existing on the shelf below, though it is now almost entirely con- verted into a peat-bog with a small pond in the middle (see fig. 2). Fig. 2.—Section across Hard Tarn. H.T.=Hard Tarn. | P=Pond. B= Peat Bog. S =Screes. Below the dip-slope of Hard Tarn is an escarpment; similar to that seen above. The accompanying plan (fig. 3) shows the nature of Fig. 3.—Plan of Hard Tarn. (Scale: 5 feet =1 mile.) bare glaciated rock below , aN HD C Mie x= Deepest point. d= Delta. E=Normal exit over screes. CC= Cliffs. S=Swamp. W.E.=Wet-weather exit over rock. the tarn and its surroundings. The deepest part of the tarn at # is only 3 feet, and the greater part of the northern side varies in ‘Vol. 52.] MR. J. E. MARR ON THE TARNS OF LAKELAND. 15 depth from 3 to 2 feet, the tarn gradually shallowing towards the south. The normal exit is at the western end, by a stream running through screes (#), and although these screes form so insignifi- cant a feature in the landscape that they might readily be overlooked, and the rest of the lake is surrounded by solid rock, actual measure- ment revealed the fact that the shortest distance from rock to rock ‘near this exit was about 25 feet, so that there is little doubt that this tarn owes its existence to the blocking of one end of a sloping dip-slope between two escarpments by screes. A feature of particular interest was noticeable at the time of my visit after heavy rains. Another stream ran from the middle of the southern side of the tarn from the abnormally high lake-level, over the lower escarpment, along a shallow groove. As this groove must be gradually deepened during wet periods, while the screes are increasing at the exit, the time will arrive when this tarn ceases to be one having its exit over loose material, and sends its surplus waters permanently over the solid rock. We have here an intermediate stage in the “process of formation of such tarns as Codale, described in my former paper. (c) Hayeswater. I examined this large tarn lying below High Street, and south- east of Patterdale, because, in the discussion upon my former paper, it was cited by Dr. Mill as a possible connecting-link between the tarns and the valley-lakes. It lies at an elevation of 1383 feet, and the last rock seen in Hayeswater Beck, which issues from it, is near the point where the 1250 feet contour-line crosses the beck. The tarn might well be deeper than 133 feet, and still be drift- dammed, for the hill on the left bank of the gill has a thick bank of drift running far down Hayeswater Gill valley, and a buried valley of great depth might well exist beneath this. In many places, Hayeswater Beck seems to be cutting its way between rock and drift, as described in the case of the stream from Brund Fell, near Rosthwaite. Hayeswater therefore presents no indications of lying in a rock-basin. (dq) Angle Tarn, Patterdale. This tarn lies on a plateau beneath Place Fell. It is evidently - quite shallow, for numerous boulders project above its surface in different parts, and it is hardly likely that anyone would claim it as a rock-basin, with its numerous rocky bays, its two islands and peninsula. It was formed by the stopping of a depression starting from the northern end of the tarn, and running round the rocky knoll north of the present exit, to join the beck proceeding from this exit, a short distance west of the tarn. 16 MR. J. E. MARR ON THE TARNS OF LAKELAND. [Feb. 1896, Discussion. Dr. H. R. Mitt said that he was much interested in the Author’s observations, especially those on Hayeswater. He wished that there were facilities in the meeting-room for optically projecting photo- graphs, as a photograph he had taken from the top of High Street showed the glacial accumulations in the narrow valley very distinctly. As Mr. Marr had found every tarn that he examined to be held in by a barrier of drift, it seemed very likely that most, if not all, of the larger lakes would be found to owe their origin to the same cause. In this connexion it was worth mentioning that Prof. W. M. Davis, of Harvard, considered, from the configuration of the larger lake-basins in the district, that they were produced in drift-blocked valleys. The AvutHor thanked Dr. Mill for his remarks. He observed that even if Hayeswater were abnormally deep for mountain-tarns, there was sufficient drift to block it. He had already written a paper on the origin of the larger lakes of Lakeland, and submitted it to another Scciety. Vol. 52.] THE ROCKS OF THE LIZARD DISTRICT, 17 3. The SERPENTINE, GNEISSOID, and HornBLENDE Rocks of the Lizarp Disraict. By T. G. Bonnzy, D.Sc., LL.D., F.RS., F.GS., Professor of Geology in University College, London, and Fellow of St. John’s College, Cambridge. (Read November 6th, 1895.) [Puate I.] ConTENTS. Page BPPMIMOGICLOEY, Ff copacanonnsansocs aqrerencedasasennisine ss SS SSS es a ae end of the Cove we found an inclusion of nearly pure, rather coarsely crystallized hornblende. It is about 6 or 7 inches thick in the part drawn (fig. 2, p. 20): the ordinary hornblende-schist bending round it, as-indicated, but it ‘trails out’ to the right and, interruptedly (there are two layers), to the left. In this direction, at about the same level, are two or three similar but smaller inclusions. A slice from the largest inclusion ’ shows it to consist almost entirely 1 Quart. Journ. Geol. Soc. vol. xxxix. (1883) p. 4; see pl. i. fig. 2. - ® Ibid. vol. xlviii. (1892) p. 122. ; 3 Op. cit. pp. 184-138, af. p. 124. * 4 T saw about four instances —varieties of linear streaking were countless. ° The specific gravity of the specimen, as determined with a Walker’s balance, is 3°124 ; the mean of two specimens of fairly normal hornblende-schist is 2°748. I am indebted to Miss Raisin for these and other determinations in this paper. T ensure accuracy, each of us read the balance. c2 20 PROF. T. G. BONNEY ON THE [Feb. 1896, of a dull green, rather strongly pleochroic hornblende, in somewhat irregularly-formed crystals, commonly much speckled with minute and elongated specks of iron oxide. Some larger granules of the latter mineral occur, with a little rutile and possibly pseudobrookite. Besides, there are a few isolated grains or granular patches of a clear Fig. 2.—Eye of hornblendite, included in banded hornblende-schist. (Northern side of Porthoustock Cove.) LAY Rey ap ess one (hy 2% Gi WA nia a = banded hornblende-schist. b = coarsely crystallized hornblende. mineral : this has rather a high refractive index and low polarization- tints for a felspar, an extinction, I think, oblique (it is difficult to get any line from which to measure), and it may perhaps be a colourless epidote. These inclusions, though on a much smaller scale, recall to mind those which we found so common in Sark.* (6) Inclusions in the Hornblende-schist south of Kilcobben Cove. Here also the rock is frequently streaked, and instances of resemblances to current-bedding are by no meansrare. Near to the northern side of the promontory we found long lenticular masses of rather coarse hornblendic rock, such as is described above, lying with their flat sides roughly parallel with the dominant banded structure, They are seldom more than 2 or 3 inches thick, but are sometimes 2 or 3 feet long and almost as wide.’ From this size they may be found down to little patches, almost streaks. (c) Quarry on the descent to Mullion Cove. This quarry, noticed in the paper of 1891,* was in a better con- dition for study at the time of our visit in 1894. The rock here is generally coarser in structure than any other mass known to us in the Lizard peninsula. Most of it shows a banded structure, which, 1 Quart. Journ. Geol. Soe. vol. xlviii. (1892), p. 128, ete.; see also vol. xliii, (1887) p. 324. 2 In aslice from one of these I find nothing but hornblende, like that described above, and a little iron oxide.. But the rock was very difficult to cut, and the slice is a rather thick one, > Op. jam cit. p. 479. Vol. 5 Be ROCKS OF THE LIZARD DISTRICT.. 21 however, here and there disappears, for it passes into a ‘spotty’ one. But the general condition of comparatively coarse crystallization is replaced, locally and rapidly, by a finer one; the latter exactly resembling the normal hornblende-schist, whether banded or ‘ dioritic,’ which occurs elsewhere at the Lizard. Fine-banded and coarse-banded portions may be seen, one within a foot of the other. Of the latter variety, bands, quite ; inch thick, consisting almost wholly of felspar, can be traced frequently for more than a foot in length ; bands also, both light and dark, sometimes quite 4 inch thick and occasionally more, run continuously for 8 or 9 inches at least. One part of the rock presented a curious resemblance to false bedding, but a closer examination showed that this might be equally well produced by a shearing movement in the mass. In another place the bands were overfolded, and appeared to have become displaced by a ‘strain-slip’ movement. The latter, no doubt, might be produced after the solidification of the rock, but the general appearance of the former structure and the absence of divisional planes suggested. that it was due to a sliding movement, while the mass was still more or less viscid, so that the ruptured surfaces had become cemented during the last stage of crystallization. The irregular and sporadic passage from the banded to the spotty condition also seemed difficult: to explain if the former were due to an original stratification of clastic materials, but seemed easily explicable on the hyp6thesis that movements had taken place in a magma, after some constituents had separated, but anterior to the complete crystallization of the mass; this had caused the ordinary ‘ granitic’ structure of a holocrystalline rock to be replaced in many parts by a banded one. It has, however, been suggested that these linear structures are due to a yielding—more or less local—in a coarse holocrystalline rock when subjected to pressure. Apart from considerations which I have elsewhere noticed,’ I had this hypothesis always before my mind and found it inapplicable as a general explanation, though I should admit the possibility of its accounting for a certain ‘slabbi- ness’ occasionally perceptible.2 The effects of dynamo-metamorphic processes, in the ordinary sense of that long word, can be studied at the extreme south and in a more limited area at Porthallow, as described in our former paper, and the conclusions then formed were strengthened on the present occasion by tracing, especially in the first-named district, the gradual change from the normal horn- blende-schist to the pressure-modified ‘green schist.’ If then the ordinary banded hornblende-schist of the Lizard owes its structure to ‘dynamo-metamorphism,’ recrystallization must have subsequently occurred to such an extent as to destroy every characteristic of that process. ‘T’o concede this, I may observe by the way, would be fatal to every attempt to implicate the schist and the serpentine in an ‘igneous complex,’ for the latter rock, as a rule, exhibits no sign of 1 Quart. Journ. Geol. Soc. vol. xlix. (1893) p. 94, and vol. 1. (1894) p. 279. ? But, even if this be due to a very slight shearing, its parallelism with the banded structure and consequent low hade (universal features, so far as I know) are by no means easy to explain. 22 _ PROF, T. G. BONNEY ON THE [Feb. 1896, crushing or of recomposition, whether as serpentine or as peridotite. The breadth and persistency of the bands in this hornblende-schist, as I have more than once pointed out in similar cases, are further difficulties in the dynamo-metamorphic hypothesis. In order to obtain by crushing bands such as those described above, the original rock would have had to be almost incredibly coarse ; yet such bands are not infrequent both at the Lizard and in Sark. As regards the ‘stratification’ hypothesis which I formerly ac- cepted, I may mention a difficulty, the gravity of which has increased with my experience. If the rock originally were a basic tuff (and no other materials would give us the appropriate chemical com- position), the conditions of deposit must have been very exceptional. Undoubtedly, beds of fine-grained ash occasionally exhibit great regularity of structure, but commonly this is speedily interrupted by the setting in of coarse material, the rock becoming ‘ knubbly’ if not agglomeratic. But these hornblende-schists are singularly free from blotching or irregular spotting’; the bands of different mineral composition alternate just as the arenaceous and argillaceous layers at Morlaix in Britanny or Port Erin in the Isle of Man. This difficulty might, indeed, be eluded by supposing the materials to have undergone metamorphism so extreme as to dissociate the constituents of the bits of tachylyte and the lumps of scoria, and that to have been followed by an orderly process of segre- gation somewhat analogous to what occurs in the formation of flint, converting ultimately the rather heterogeneous materials into fairly uniform mixtures of minerals not at all minute. This hypothesis, however, though obviously a possible one, obliges us, as I feel more and more strongly, to assume conditions which are so exceptional that they can hardly have prevailed over such large areas. Hence I am forced to adopt the other hypothesis.” III. Tas Genesis of tHE ‘ Granuxitic Grove.’ On this subject fewer words are needed. I may content myself with saying that the result of this visit has been to strengthen my confidence in the correctness of the explanation adopted in our last paper,® namely, that these banded rocks have been produced, as probably most banded gneisses have been produced, by fluxional movements in a heterogeneous magma; the cause of heterogeneity in this case being, as in the one described in Sark,* the intrusion of an acid into a more basic rock, by which the latter has been 1 The nearest approach to this is the case near Mullion Cove, described above, and even here there is nothing resembling the irregularity which is usual in volcanic ashes. * It also accords better with that which is now generally adopted for the granulitic group. This is supposed to be almost in the condition which it assumed on consolidation ; but its darker member is sometimes not very different from corresponding parts of the hornblende-schist, so that one can hardly assume the two rocks to have had totally diverse origins. 3 Op. cit, vol. xlvii. (1891) p. 477. 4 Op. cit. vol. xlviii. (1892) p. 132. Vol. 52. | : ROCKS OF THE LIZARD DISTRICT. 23. softened, drawn out, and even locally melted down and absorbed by the former. One section, which I found on the southern side of Kennack Cove, so well illustrates this process that it deserves, perhaps, a brief description. A light-greyish granite is intrusive into .a dark dioritie rock, which it has shattered into a breccia, but in places one can see that the latter is locally melted by and incorporated ‘with the former, the result being a regular, rather fine-grained, streaked or banded gneiss. I obtained specimens of all three rocks and have examined them under the microscope. The granite consists mainly of quartz and felspar, with a rather small amount of biotite (somewhat bleached)? The structure is granular, only one or two of the larger felspars showing any approach to a crystal-outline, and the grains differ much in size. It exhibits the association of ‘this mineral and the quartz to which I have often called attention as more characteristic of a gneiss than a normal granite,’ with a ‘very slight approach to a linear order in the constituents, The dioritic rock consists of felspar, rather decomposed, apparently plagioclastic, green hornblende, biotite (not much, and rather sporadic), with a little sphene, etc. The structure is granular, -with occasionally an approach to ophitic, and felspars, 4 or 5 times the diameter of the rest, occur sparsely. The banded gneiss has a general resemblance in structure to the granite, except that its felspars are even more variable in form and size, the linear ordering of the constituents is more marked, and grains with micropegmatitic structure, which are rare in the other rock, are common here; apatite is more conspicuous and two or three very small garnets occur; there is a considerable amount of a rich brown biotite, but hornblende is absent; at least I do not find a single scrap (there are a few green flakes) that I can identify with certainty. On the significance of this I have already written.* Additional evidence, however, was obtained in regard to one point of interest. I have always believed the granulitic group to overlie the hornblendic, though I felt that the evidence in favour of this was not very strong. The latter rock usually occurs in great continuous masses, the former in more or less interrupted blocks, which, though they may be sometimes traced with but little inter- ruption for considerable distances, are associated (always so far as I remember) with the serpentine, and occur in such a manner as to give the impression that they are fragments of a mass which it has shattered, and in some cases actually transported. In one place, however, in the crags on the south side of Cadgwith Cove, as men- tioned in our former paper,’ the granulitic rock appeared to be superposed on the hornblendic schist. On the last occasion, favoured 1 The specific gravity of the granitic rock is 2°611, of the dioritic 2:917, of the banded gneiss 2°628: intermediate, but,as we might expect from its appear- ance, nearer to the first. 2 In these descriptions and throughout the paper, minor details of composition and structure are suppressed, as being without significance for my main purpose, 8 Quart. Journ. Geol. Soc. vol. xxxvi. (1880) p. 97, ete. 4 Ibid. vol. xlviii. (1892) p. 132, 5 Ibid. vol. xlvii. (1891) p. 478. 94 PROF. T. G. BONNEY ON THE [Heb. 1896, by a calm day, we closely examined, from a boat, the whole line of cliffs from Church Cove to Cadgwith. We found that, after passing the huge mass of hornblende-schist which forms the crags of Carn- barrow and the gloomy portal of Dolor Hugo, the rock, on approaching the archway leading into the ‘Frying Pan,’ continues, for some distance above the sea-level, to-be a true hornblende-schist, but that: there are, in the upper part of the cliff, several reddish granitic veins, the direction of which appears to have a rough correspondence with the structure of the former rock, while the cliff above these assumes amore ‘granulitic’ aspect. On the southern side of the entrance to the ‘ Frying Pan,’ a fault, or group of faults, brings serpentine and typical ‘ granulite’ against hornblende-schist. But, immediately beyond the archway, the headland between it and Cadgwith Cove presents the following section. The upper part of the cliff, beyond. all question, consists of the granulitic rock; while the lower part, at the south-eastern corner, for a considerable height above the sea, is no less typical hornblende-schist. The two rocks gently descend in a northerly direction until, near the north-eastern angle, the hornblende-schist gradually disappears beneath the water and the mainland crags consist wholly of typical banded granulite; though even here the hornblende-schist still appears in some skerries very near to the shore. Passing round into the cove, we find that its southern side, as we formerly stated, consists mainly of the ‘ granulitic group, but that near the water’s edge the rock generally is a horn— blende-schist.!_ No sharp line can be drawn between the two groups, but between the well-banded and thoroughly typical representatives: of each there is usually a zone from 7 to 10 yards in thickness, rather neutral in character: veins of a reddish granitic rock, breaking, on the whole in a horizontal direction, through a dark rock which now and then resembles the basic member of the granu- litic group more closely than the dark part of the hornblende-schist.. Obviously, if both these groups are igneous in origin, this super- position cannot count for much. It may, however, have the signi- ficance, that, on the assumption of the hornblendic rock being the earlier extrusion, the upper part of its mass would offer less resist-- ance under ordinary circumstances to the passage of an intruder. Hence the phenomenon may have a bathymetric significance, if it. has no other. , LY. Renarions oF THE SERPENTINE TO THE ‘GRANULITE’ AND TO THE HoRNBLENDE-SCHISTS. Before discussing the group of sections near Ogo-dour and east: of the Lion Rock, from which my friends have drawn certain con- clusions,’ I must make a few remarks upon the general principle, which, as it appears to me, is implied, if not actually enunciated in 1 Tt is regularly banded, the white felspar and dark hornblende showing 2 hypophitic structure, and differs only from the most normal hornblende-schists: in becoming here and there slightly micaceous. x 2 Quart. Journ. Geol. Soc. vol. xlix. (1893) p. 210. Vol. 52.] ROCKS OF THE LIZARD DISTRICT. 25 their paper.1 It amounts to this: that in an extensive district, where the rocks exhibit many difficulties and complications, each section or limited group of sections can be regarded by itself and be made the basis of induction, independently of all the others. But here, unless I mistake, lurks a fallacy, the nature of which will be readily perceived by considering a particular instance as an illustra- tion. Suppose the question to be whether an igneous rock is intrusive into or contemporaneous with a group of sedimentaries. Suppose, further, that in 11 out of 12 sections the evidence is inconclusive, but that the remaining one gives a decisive answer on the one side or the other. Then there would be no room for furtherdoubt. The uncertain- ties of the eleven would count for nothing against the positive evidence of the one section. Suppose, however, that, of the 12 sections, the evidence of four or five is rather more favourable to one conclusion ; that of two makes any other highly improbable, while that of one appears to accord better with the contrary conclusion; and the remainder give no answer at all. We cannot regard the testimony of this one unfavourable witness, as if the others were non-existent. Certainly no judge, probably no jury, would act upon such a principle. The apparent conflict of evidence undoubtedly calls for a careful cross-examination of each witness, but in such a case as we have mentioned it is surely far more probable that the one section should have been misunderstood than that a contradiction should exist. The more specious interpretation does not always turn out to be the true one, and we must proceed in our attempts to learn the secrets of Nature as men who are seeking to decipher inscriptions, where the language is dead and the characters are obsolete. It may be said, however, that the ordinary laws of inductive reasoning do not apply to this particular case, because we are dealing with an ‘igneous complex.’ The term undoubtedly is an attractive one; there is a certain mystery about it, but there is also, as in all mysteries, a certain vagueness. ‘Complex’ means a tangle, and thus is a term which fails to explain anything ; to fall back upon it, is a confession of defeat and an admission that when Nature plays the Sphinx we decline to take the part of Cidipus. In the case before us, however, the authors’ meaning may be inferred from _ certain conclusions which they have formulated.? These, briefly stated, amount to this: that in the cliff and on the adjoining shore, east of the Lion Rock, the serpentine is traversed by basic dykes, which pass locally into hornblende-schist, and besides this put on, in the thicker portions, appearances which are characteristic of the ‘ granulitic group’; also that there is a wedge-shaped mass of this granulitic rock, which exhibits a structure incompatible with the hypothesis that the serpentine was intruded after the mass itself became solid. In regard to these conclusions, I may venture at the outset to make the old comment Dolus latet in generalibus. (a) ‘The dykes pass locally into hornblende-schist.? Yes, but into what horn- Op. cit. p. 200. 2 Ibid. p. 210. 26 PROF, T. G. BONNEY ON THE [ Feb. 1896, blende-schist ? Is it the same as the rock which forms the great cliffs of Carnbarrow and Hot Point, of Housel Bay, and Predannack Head, not to mention other places? By no means, I should say. True, the dominant minerals are the same in both, and these dykes exhibit locally a trace of foliation. That is also true of other dykes in this region’; nevertheless, the hornblende-schist proper, as a rule, is a very different rock, even macroscopically. It iscommonly more or less banded, almost always distinctly ‘linear’ in structure; only rarely and only very locally would there be any difficulty in dis- tinguishing the one from the other. I find that the same holds good ef the microscopic structure of the two rocks; the differences can hardly be expressed in words, but asa rule they exist. What, then, does this prove? That sometimes, if we take two hand-specimens, carefully selected from two groups of rocks, differing in age and history, we may be unable to distinguish the one from the other, because neither presents characters upon which we can fasten for that purpose. We might as well affirm that the Greek and the Latin uncial alphabets belong to the same language because certain letters in the two are identical. Has any one of these dark pyroxenic dykes in the Lizard region exhibited such a banded structure as that which occurs again and again in the ‘hornblendic’ group? It would be, in my opinion, just as reasonable to contend that the hornblende- schist was only a modification of the gabbro,* because now and again, though very locally, resemblances can be detected; or that all the basalt dykes of Scotland were of one age, because it is not always easy to say whether a particular one belongs to the Paleozoic or to the Tertiary era. (6) ‘The dykes near the Lion Rock, in their thicker parts, sometimes resemble the granulitic group.’ To this we may reply in terms similar to those already used. Once or twice a dyke may be found to exhibit some rather irregular fel- spathic veins or seams. But this, so far as my experience goes, is not a very uncommon feature in districts such as the Lizard. The resemblance between the two rock-masses seems to me hardly closer than the notorious one between Monmouth and Macedon. I have found it difficult in other places to distinguish between veins of infiltration and of intrusion, yet this does not prevent me from believing that each really exists, and can be often identified. So that im this case also, while I grant that certain resemblances may be found, I deny that they are sufficient to warrant the conclusions which have been drawn from them. (a) Relations of the Serpentine to the Granulitic Rock. But I pass from generalities to particulars, and first to ‘the wedge-shaped mass of typical granulitic rock.’ There can be no question that this—like the great masses which crop up on the ~ 1 Quart. Journ. Geol. Soc. vol. xxxix. (1883) p. 6 (reference). 2 Tf so, there should be no ‘complex,’ for the gabbro cuts the serpentine again and again. . Vol. 52.] ROCKS OF THE LIZARD DISTRICT. 27 shore some little distance to the south, belongs to the granulitic group. The drawing which my friends have given is substantially accurate!; the inference also which they draw is correct, but only in an extremely limited sense—in other words, everything turns upon the exact meaning at- ith tached to the phrase ‘solid Fig. 3.—Projection from the egranulitic rock.’ Taking that granulitic mass included wm mass as a whole, its darker serpentine. (Hast of the Lion bands indicate firstly, the for- Rock.) mation of a banded or rather a streaky structure, and secondly the contortion of the same’; but, so far as I could see, no connexion exists between these structures as a whole and the external shape of the mass, and there is nothing to difference this block from those which occur, as I have said, to the In all these diagrams the serpentine is ae one a ‘aa oe dotted, and the fine lines indicate the os pine ee Me more micaceous bands in the granu- only rather curiously con- litie rock. torted, but this structure is not very uncommon in the granulitic group, and I was unable to see that any relation existed between either it or the shape of the mass and the serpentine, or to find evidence either that the granu- litic rock was intrusive in the serpentine or that the two had been folded together, as the result of earth-movements while both were in a plastic condition. As is stated above, there are two large masses of the granulitic rock on the shore towards the south. These, how- ever, are not wedge-shaped intrusions, but huge blocks; yet in places they exhibit contortions, which are hardly less pronounced than those in the other mass.* ‘The serpentine in their neighbourhood exhibits a slight foliation, which dips at a high angle to a point a little W. of W.N.W., but this neither makes the rock fissile, nor produces any marked effect on its microscopic structure, nor stands in any relation to that of the granulitic masses. : I accordingly claim a verdict of ‘ not. proven’ here, and pass on to other localities to see how far their evidence is ‘incompatible with the theory that the serpentine was intruded into solid granu- litic rock.’ At the first glance it seems possible to explain the 1 Op. cit. p. 209, fig.4. I venture to suggest two trifling emendations. At B the obtuse angle should be replaced by a blunt thumb-like projection (see fig. 3, above), and at D the serpentine occupies the wider, but not the narrower part of the inlet in the granulitic mass: the latter rock being practicaily continuous at a depth of 3 or 4 inches, as I could see in one place and feel with my fingers all along. ‘To this point I shall return. * These might be either successive stages in one process or separated by some considerable interval of time (as I incline to think). In these, however, the ‘dioritic’ rock predominates, so that it is granitic (lighter-coloured) bands that wriggle about. 28 PROF. T. G. BONNEY ON THE [Feb. 1896, relation of these two rocks by one of four hypotheses: (a) that the two rocks have been brought together by faults; (6) that the two have been folded together ; (c) that the two have flowed together ; (d) that the serpentine is intrusive in the granulitic rock.’ As the relations of the two rocks have been described in former papers, I shall not repeat what is already in print, but content myself with remarking that though I have again examined all these cases, I find no reason for altering my statements, and with describing very briefly a few other instances. As a preliminary, 1 venture to remind the reader that the granulitic rock commonly occurs as blocks, which sometimes appear to be completely included in the serpentine, but at others may be either projecting ridges or crags attached to much larger masses below or behind the visible surface. Where these exhibit a definite structure, this seems more or less to determine their outline, so that well-banded varieties are often fairly rectangular in shape; but as such a structure is not always present, considerable variety of form is possible. Though small slips and displacements are common in the serpentine, the faces of these blocks do not appear, as a rule, to correspond with faults ; moreover, the two rocks occasionally, though not commonly, are welded together—in other words, the relations of the granulitic rock and the serpentine appear to me, as a rule, incompatible with the first or the second hypothesis. As for the third, it may be understood to mean either that the two rocks have been simultaneously emitted as parts of a magma already separated in accordance with Soret’s or some other principle, or that the one material has been injected into the other, and has so completely softened it, if it were already solid, that the two have subsequently flowed on together. Now, the granulitic mass itself exhibits irregularities in structure and variations between the extremes of mineral composition, which accord well enough with the one or the other of these interpreta- tions; but between it and the serpentine no transitional condition can be found, neither does it occur in lenticular or streak-like bands, such as the third hypothesis would lead us to expect, but in blocks ; while the fourth hypothesis, as I trust will be perceived from the evidence which I am about to quote, accords better with the facts. Time, however, may be saved by noticing at the outset a general objection which might not unreasonably be raised, namely that, if the serpentine be intrusive in the granulite, its relations to the latter are rather unusual. It has formed neither dykes nor branching veins in the ‘ granulite,’ nor has it shattered that rock and caught up numerous small fragments. Yet all these are done by granite, diorite, gabbro, and other deep-seated rocks, as well as by their more compact representatives. The serpentine adopts the form, as those holocrystalline rocks often do, of irregularly-rounded bosses or somewhat elongated tongues, but it is not connected, as they very commonly are, with peripheral dykes and veins. This, however, appears to be the usual habit of peridotites and serpentines. * T exclude that already mentioned, namely, that the granulite is the intruder, because, in the cases which I am about to mention, I cannot conceive the possi~ bility of its being seriously entertained Vol. 52.] ROCKS OF THE LIZARD DISTRICT. 29 I have probably examined in the field more of these rocks—espe- cially the latter—than most geologists, yet I have never seen a branching vein, and only two or three dykes." The mode in which this rock occurs generally suggests that it was extruded in a rather ‘ pasty’ condition ; sometimes also that the temperature was not very high.” But though the serpentine does not send veins into the ‘ granu- lite,” its relations to that rock appear to me generally to suggest and sometimes to prove intrusion. Take, for example, this instance from Polbarrow Cove (fig. 4), where a fragment of serpentine about 14 inches long, 3 to 5inches wide, and seemingly about Fig. 4,— Serpentine adhering to a 3 inches thick, still adheres ‘ step’ of granulite, in Polbarrow to the granulite, which is Cove. particularly evenly-bedded (reddish grey with dark- coloured) for about half a yard above and a yard below. Some two or three yards behind the top of the craglet is another and longer mass of serpentine which appears to occur in asimilar fashion. Or this case from the same cove (fig. 5), where the junction-surface is ir- regular, the granulite for a short distance is disturbed, and two or three small fragments of it occur in the ser- Fig. 5.—Banded granulite (with fragments pentine. Or this one in serpentine), south of Poltesco Cove. from Enys Head, where the serpentine seems to have forced open the granulite along the lines of banding, rumpling those in its imme- diate neighbourhood (fig. 6, p. 30). Orthis other one from the same locality, where the junction-surface is puckered and squeezed up, while in one case (as shown in fig. 7, p- 30) the bands of the granulite are cut off by the serpentine. We found another, and a very marked instance of the same kind, 1 T do not forget the case in Forfarshire described by Sir Charles Lyell, but I have not been in that part of Scotland. 2 I may add that in districts where the rocks have undergone much mechani- cal disturbance, the junctions, as a rule, are spoiled. Serpentine is a brittle rock, and commonly ‘yields to strains before its neighbours, so that a line of junction is generally a line of fracture, and often of complete ‘smash.’ This rule is almost universal in the Alps. 30 PROF. T. G. BONNEY ON THE [Feb. 1896, near the White Rock, a little above sea-level, and the projection with bent bands (fig. 8) occurred, like those Fig, 6.—Serpentine and banded granulite, above, in Polbarrow Enys Head. Cove. I have, in- deed, sketches and notes of not a few Similar cases in my journal, but forbear to multiply like figures and statements. I must, however, once more refer* to the remarkable mass in the quarry at Kildown Point, which again has been most care- fully studied. Before the excavation was made, it must have been wholly or almost wholly enclosed in the serpentine. That rock still rests in places on the top; , it forms one or two small tongues Fig. 7.—Serpentine and banded between the bands of granulite, granulite, Enys Head. and a blunt lobe at the base of the southern side, where some of these bands are bent and inter- cepted. Yet in the immediate neighbourhood of this mass the serpentine does not show the slightest sign of crushing ; it is in a perfectly normal condition, while that in the lobe, though rotten, exhibits a slightly streaked or foliated structure, which, however, makes a high angle with the horizon, though the bands in the granu- lite are inclined at a low angle to the same. But this is not all Fig, 8.—Serpentine and banded the evidence. Masses of granu- granulite, Polbarrow Cove. lite appear to crop out from the serpentine on the almost pre- cipitous slope below the quarry. The descent of this would be so hazardous that I have never made the attempt; but this year I managed to land from a boat in a little cove at the base of the cliff. Here we find granulite 1 Compare also the projecting mass of granulite in the included mass east of the Lion Rock (fig. 3, p. 27), and note the outlines of the granulitic part and of the micaceous bands. 2 Quart. Journ. Geol. Soc. vol. xlvii. (1891) p. 469; see also vol. xxxiii. (1877) p. 899. Vol. 52.] ROCKS OF THE LIZARD DISTRICT. 31 forming the southern, and serpentine the northern side of the cove, and in the middle part a mass of granulite through which in more than one place serpentine ‘ breaks irregularly, exactly as it would break through a rather hard sedimentary rock, in places forcing back and crumpling up some of the bands.’* One mass of serpentine, of which I made rough sketches, was about 4 yards long and2wide. That also showeda slight foliation or fluxional structure, and this too was nearly at right angles to the bands in the granulite. All the way up the crags above this place we see outcrops both of the one rock and of the other. I submit then, that these instances (and it would be easy te go on multiplying them) show that the serpentine is really intrusive in the ‘granulite.’ The former rock, however, must have been at this time only in a semi-fluid condition—viscid and tough—so that it was not able to do more than force its way occasionally along planes of weakness in the ‘ granulite’ (blocks of which it often included and perhaps tore away), softening the latter rock locally and squeezing -it about, though the effect which it produced generally extended only for a few inches away from the actual junction- surface. (b) Relations of the Serpentine to the Hornblende-schists. The best sections for studying these relations, so far as I know, are at ‘ Potstone Point,’ on the cliffs north of Ogo-dour, and at Hen- scath, on the west coast; at Carnbarrow and in Porthallow Cove on the east. Except the first, these were well known to me, and of it I had a general knowledge. All, however, have been carefully examined. First, with regard to the Potstone Point sections, of which Messrs. Fox and Teall have given so admirable an account.” These lead, in their opinion, to sundry conclusions, of which I quote three,® as the rest need no further discussion :— ‘(1) The hornblende-schist and serpentine of the Ogo-dour district form together a banded complex of crystalline foliated rocks. ‘(2) The relative ages of hornblende-schist and serpentine cannot. be satisfactorily determined, but the occurrence of lenticles of serpentine in hornblende-schist points to the conclusion that, if there be any difference in age, the serpentine is the earlier. ‘(3) The complex of schist and serpentine has been folded after the banding was produced, and before the dykes were intruded. Some, if not all, of this folding probably took place when the com- plex was formed.’ Of these the second and third alone are important, because without them the first, so far as I understand the word ‘ complex,’ commits us to very little. In this locality also the question between us is one of interpreta- tion rather than of facts. I gladly avail myself of the opportunity * Quoted from notes written on the spot. ? Quart. Journ. Geol. Soc. vol. xlix. (1893) p. 200. 3 Ibid. p. 210. 32 PROF. T. G. BONNEY ON THE [Feb. 1896, of expressing my admiration of the map published in Messrs. Fox and Teall’s paper.! The making of it must have been no easy task, for the slope is very irregular, broken, and sometimes not the place for an unpractised climber. So accurate are both it and their descrip- tion that I had no difficulty in following them step by step in going over the ground. This, then, is how I interpret the sections. Nowhere in the serpentine can I find any of those symptoms, so familiar to me, which indicate that after solidification it has been subjected to severe mechanical disturbances (dynamo-meta- morphism. The two cases, figured by my friends * (and the number of such is small), appeared to me due to a different cause. The intru- sion of a hot viscid mass into one already solid suffices sometimes to bend either the latter locally or pieces of it which have been torn off. Here there is no sign of the two rocks being folded as solids. Furthermore, here and there, the serpentine includes slabs of hornblende-schist of normal aspect, or the junction of the two rocks may be often seen (as will be presently described), to be perfectly welded and yet distinct. In one case (fig. 9) the serpentine runs up to the broken edges of a wedge- like projection of the horn- blende-schist. In the latter rock the banding is regular, only a little rumpling and flexure being perceptible at two places, which are respec- tively 2 feet and 4 feet in a line from the point of the former rock, while the mass as a whole is not affected. The disturbance, in short, reminds one of the crumpling which might be produced by thrusting the thicker end of a flat paper- knife between the pages of a Fig. 9.—Banded hornblende-schist in serpentine, Potstone Point. The dotted rock represents serpentine, tightly-closed book. The ser- pentine in parts of this ‘ com- plex’ appears to be sometimes the lines indicate diagrammatically the banding of the hornblende- schist. impure and harder than it ought to be; often it is streaked like a brownish slag, while here and there a thin band can be discovered, which resembles hornblende- 1 Quart. Journ. Geol. Soc. vol. xlix. (1€93) p. 203 (I had it with me as I worked). Once or twice I felt doubtful about the small faults, and should have made a slight change as to a dyke; but these are insignificant details, and I, not they, may be wrong. * Op. cit. p. 212, 8 Which explains figs. 1 and 2, op. cit. p. 202. Under these circumstances the junction-surface of the two rocks might be ‘ wavy,’ and ‘for every tongue of serpentine into schist [there would be]....a corresponding tongue of schist into serpentine.’ In such cases also the two rocks would probably exhibit a parallel foliation. This does not appear to have occurred to my friends, and I find no evidence that they minutely investigated the structure of the serpentine, in which, however, the key of the position is to be found. Vol. 520] ROCKS OF THE LIZARD DISTRICT, 33 schist, and seems to pass rapidly into the adjoining serpentine.’ In the field I came to the conclusion that the latter rock had intruded into the former, occasionally breaking off pieces of it and even locally melting them, wholly or in part. Let us then see how far this con- clusion is supported by study with the microscope. Taking first a slice cut from a specimen which showed (as I supposed) a junction of the serpentine and hornblende-schist, I find that the greater part consists of a serpentine (mineral) of a brownish or greenish-orange colour, exhibiting a structure which, if this were an acid rock, I should not hesitate to claim as fluxional. In this groundmass are scattered clear grains of a mineral without definite external form or any well-marked cleavage, which, however, I think may be identified as a hornblende, together with one crystal of a serpentinized bastite, including rods of a monoclinic pyroxene. Besides these are numerous granules, often aggregated, of a fairly translucent brown mineral; some, doubtless, are picotite, but others, which exhibit double refrac- tion, are probably hematite. This part is succeeded by a streak rich in pyroxenic grains, many of them light brown in colour; and the latter rock (sometimes after an intervening film of the former one) changes to a band (slightly irregular in outline) consisting of felspar, in a very decomposed condition,” of hornblende, warm brown in colour, and of a moderate number of grains, which probably are a white augite, though the mineral is rather ‘ dirty’ and sometimes serpentinized. This band is about 1 inch wide, and the slice then is ended by a serpentine like that already described. But on examining the hand- specimen, this serpentine appears to be little more than a film, for in not more than one-fifth of an inch we find fairly normal horn- plende-schist. Next let us take two specimens from a part of my friends’ section * near the porphyritic dyke. It is thus described in my notes :—‘ A curiously banded and streaked rock, exhibiting fine eompact bands and coarser-looking brown bands, in parts much wrinkled and once or twice slightly brecciated, somewhat resembling serpentine, but rather harder than is usual with that rock. I havea strong suspicion that this is a mixture of serpentine and horn- blende-schist, the latter being partly melted down by and carried along with the former.’ Of one specimen, cut where the streaky structure is much curved, one would claim part, without hesitation, for hornblende-schist. It exhibits (Pl. I. fig. 5) the usual rather granular structure, and consists mainly of a felspar, somewhat de- composed, and hornblende, which, however, is brown instead of the ordinary strong green colour. In other parts (streaks) we find the grains of brown hornblende in a ‘matrix’ of composite microgranular 1 I suppose, of course, that the serpentine was a peridotite at the time of the intrusion. This must be understood throughout. 2 It is whitish by reflected light, earthy brown by transmitted, and shows specks of brightest colour with crossed nicols. ° Op. cit. p. 203 (map). I think it is from the part S and Sch below the eo marked ¢. Whether this be the top of a ‘dome’ or not, I believe it to an included mass, or, at any rate, to indicate intrusion on the part of the serpentine. Q. J.G.8. No. 205. D 34 PROF, T. G. BONNEY ON THE [ Feb. 1896, minerals; in others this ‘ matrix’ is the orange-coloured serpentine already mentioned. Other streaks consist of this serpentine with rather small pyroxenic grains. All these varieties are associated in a slag-like fashion (PI. I. fig. 6). A slice from another specimen, rather’ more serpentinous in aspect, exhibits a junction of two kinds of rock.. One presents the general structure of a hornblende-schist, but the grains of that mineral are brown, while the others, instead of being” felspar, are commonly a brownish-orange or greenish serpentinous: mineral, which in some cases, when examined with crossed nicols, resembles a bastite, in others prove to be a granular aggregate. The other kind of rock exhibits a very marked fluxional structure in a matrix (if one may so call it) which seems to be composed of minute: doubly-refracting minerals, and its bands are darkest when parallel. with the vibration-planes of the crossed nicols. Thisis spotted with -a brown hornblende, which occurs both in granules and in grains of . the usual size, and the above-named structure is almost at right angles to a very slight parallel ordering of the grains in the other part (Pl. I. figs. 3 and 4). This, however, is not all. Let us examine a piece of hornblende- schist which was included in the porphyritic dyke.’ It is a fairly well-banded variety, thoroughly typical, except that it is a little duller or of a more ‘greasy’ aspect than is usual.? Under the microscope we find a rather marked difference between the bands. Those which are lighter coloured in the hand-specimen, and are spotted with white in reflected light, consist of a very decomposed felspathic mineral, and of pyroxenic minerals, some (the less nume- rous) brown hornblende, others a pale green rather fibrous hornblende, and yet others consisting of aggregates of minute minerals. In certain bands the brown hornblende dominates, and some felspar still remains, while in yet another band the granular structure has. wholly disappeared, and the rock consists of numerous colourless flakes or prisms (about :02 inch long), which have the extinction of actinolite, and are set in a mass of smaller flakes, probably, in part at least, a white chlorite. Here then a specimen of hornblende- schist, once normal, which has been affected by ‘ contact-metamorph- ism,’ unites the characteristics to which I have just called attention and those mentioned in our last paper,’ as belonging to supposed 1 A specimen of this dyke, taken from close to the included hornblende-schist, has been examined with the microscope. In one part of the slide there are indications of mechanical disturbance. This, however, is almost certainly due to some accidental cause, such as a slight faulting, which escaped notice in the field; for the porphyritic felspars are uninjured, and the other parts exhibit a hypophitic structure. The felspar is generally decomposed, and the augite has been replaced by a dirty-looking secondary product, which shows a composite structure with crossed nicols. The rock is readily distinguishable from the horn- blende-schist. 2 Its specific gravity is 2°917, that of a speckled variety from 8S. of Kileobben: Cove 2°986, that of a banded (epidotic) variety from Church Cove 3:074. The specific gravity of the serpentine in this district is 2°730 (pit between Mullion and Lower Predannack) and 2°766. The specific gravity of two of the specimens: of the streaky rock described above is 2-935 and 2'954. This is significant. § Quart. Journ. Geol. Soc. vol. xlvii. (1891) pp. 472-783. Vol. 52.] ROCKS OF THE LIZARD DISTRICT. 35 cases of contact-metamorphism produced in hornblende-schist by serpentine. But before quitting this subject I must again refer to the locality near Pare Bean Cove, north of Ogo-dour,' where I have already asserted the serpentine to exhibit true intrusive junctions. Again, perhaps for the fifth time, I studied this rocky slope with scrupulous care. Here the serpentine has forced itself in a rather irregular fashion through hornblende-schist, though it conforms on the whole to the banded structure in the latter rock, slabs of which appear occasionally to be broken off by and caught up in the serpentine.” In this part the serpentine, which is sometimes streaked, and in which the bands occasionally present some resem- blance to hornblende-schist, is very rotten, but at a short distance the rock is in better condition. A few yards to the west of this complicated area,’ a gully exhibits the junction of the principal masses of serpentine and of hornblende-schist. Here, as shown in the annexed figure (10), a slab of hornblende-schist is separated from the main mass by a , ‘sill’ ofserpentine. Thisslab, Fig. 10.—Gully north of Ogo-dour. where it was drawn, was about Intercalation of serpentine and 32 inches thick, and it tapers hornblende-schist. away in a yard or so to less thaniZinch. That the horn- blende-schist about here is the ordinary rock cannot be doubted; it exhibits both the ‘dioritic’ and the ‘banded’ varieties. The serpentine, generally more or less decom- posed, is a little ‘platy’ in the direction of and parallel with the junction-surfaces, but this structure is in no way suggestive of crushing. The serpentine also is occasionally harder than is usual and looks 1=Hornblende-schist (more or less impure. It is locally streaked, 4 _p spe ently ze alternately warm brown and Serpentine dotted. brown-black in colour. When the included hornblende-schist becomes very thin—say not more than an inch in thickness,—it is sometimes difficult to fix upon the exact line of junction, but where it is thicker, this is generally sharply defined, and the weld between the two rocks is perfect. I have examined a specimen of this streaky serpentine (obtained from near a weld) under the microscope (PI. I. fig. 1). The darker * Quart. Journ. Geol. Soc. vol. xxxix. (1883) p. 22, and vol. xlvii. (1891) p. 470 (with General M*Mahon). 2 The bands occasionally are cut across by the serpentine. ° It could only be accurately mapped on a very large scale-map, and the trouble of doing it would not be repaid by the result. : D 36 PROF. T. @. BONNEY ON THE [Feb. 1896, bands consist of a very pale green serpentine thickly speckled with opacite or streaked with clusters of the same substance ; the lighter of the orange-coloured serpentinous mineral, mentioned above, of a colourless, but rather ‘dirty’ pyroxene,' and of barely translucent brown granules, in part at least iron oxides, more or less hydrous. In short, this rock in parts closely resembles the serpentinous portions of the Potstone Point specimen.” I have also examined a specimen of the hornblende-schist in contact with the serpentine. The fragment—from the face of the mass on the left hand of the figure—is about an inch thick. Beginning with the part farthest from the other rock, we find a band from 7 to 3 inch broad, which exhibits a granalar structure like that of an ordinary hornblende- schist, the hornblende being roundish in outline and brown in colour, and the other grains composed of an ‘ earthy’ material, no doubt replacing felspar, which, indeed, here and there can be recognized. A thin lighter-coloured band succeeds, still containing grains of brown hornblende, but with a more fibrous structure in the intervening material. This is followed by a generally similar layer, in which, however, the hornblende-grains are paler in colour, though, with the polarizer, they exhibit a brown pleo- chroism. In the remaining part of the slide (about 4 inch) the brown colour of the hornblende-grains is less conspicuous, and they are sometimes embedded in a pale-green fibrous mineral. The interval, in short, between the grains everywhere appears to be a variable mixture of minute minerals, of a more or less fibrous habit, among which I think actinolite and serpentine may be recognized, and near the very edge, where the grains of hornblende become less frequent, are dull orange-coloured patches, perhaps only staining, and the rock becomes more definitely fibrous. Granules of iron oxide, as might be expected, occur here and there in the slice. Another specimen, from a part of the adjacent hillside, where the serpentine appears to have forced its way between two slabs of hornblende-schist and to include a little streak of the latter, is very interesting. This streak is about an inch thick, and the slice has been cut through it (Pl. I. fig. 2). Beginning on one side we find a greenish, orange-coloured serpentinous mineral, in which are scattered more or less acicular microliths of a colourless hornblende. As these microliths increase in number,'the former mineral is re- placed by a more or less distinctly fibrous one, though the transition between the two kinds of rock is rather abrupt, as in the case of fluxional streaking ; then comes a brownish hornblende, rather more granular in habit, associated with a colourless mica-like mineral, probably a chlorite. Lastly, the hornblende-grains, still generally composite in structure, but becoming larger and more definite, are parted by earthy spots like the residue of felspar, and from this 1 Probably white hornblende, for the mineral occurs in all the serpentine of this neighbourhood. . 2 The specific gravity is 2°539, that of the Predannack serpentine, as already stated, being 2°766, but the difference is probably due to decom- position, Vol. 52. ] ROCKS OF THE LIZARD DISTRICT. 37 condition, as we approach the other edge of the slice, we pass back, speaking in general terms, through the conditions already described. I have again examined the sections at Henscath, Carnbarrow, and in Porthallow Cove. As regards the first and second, I could fill a page with minute descriptions, but may coutent myself with saying that I found it impossible to explain what I saw, either by displacements due to earth-movements, or by the flowing together of differentiated magmas, or by anything else than the intrusive action of the serpentine on the hornblende-schist, after the latter had become solid. As for the Porthallow sections, it may suffice (except in regard to one interesting detail) to refer to what has been already published, and to copy the words which I wrote on the last occasion in my journal :—‘‘ Some of the cases here are inexplicable to me on any hypothesis other than that of an intrusion of the serpentine into the schist. It may be said that ‘ the two have flowed together,’ but the serpentine sometimes cuts across the edges of bands in the other rock in a way which suggests direct fracture and not the result of a strain-slip. The serpentine may indeed sometimes bend with the bands, but that proves no more than that the schist (like the included fragments of gabbro near Manacle Point) has been somewhat softened and made flexible. The bending cannot be attributed to subsequent earth-movements, because the serpentine does not show the slightest. sign of crushing, and the weld between the two rocks is often perfecs.” But an examination of the specimens collected on this occasion has enabled me, as the result of the whole work, to clear up a difficulty which this Porthallow serpentine hitherto had presented. We find here and there in it, close to junctions with the hornblende-schist, grey bands, which are intermediate in aspect and hardness, Is this a less pure variety of serpentine, a streak of picrite, which, as indicated by the analysis, is present in the rock ? and, if so, how can we explain its presence?* I had hitherto vaguely referred it to some differentiation in the magma, but can now offer a more precise explanation, in accordance with the cases already described. I brought away a few specimens for further investigation. One of these, about 43 inches long, consists mostly of the ordinary Porthallow serpentine (a little redder in colour than usual) ; the remainder, a band about an inch thick, is of a greenish-grey colour, and this was in contact with, though here not welded to, a dark- grey, minutely speckled rock, which in hardness and general aspect agreed with a hornblende-schist. The latter, on examination with the microscope, exhibits traces of a banded structure; in some bands are residual grains of felspar, and with them grains of brown hornblende, but the greater part of the rock consists of flakes or longish prisms of actinolite in a felted mass of the same or of a colourless chlorite. The red part of the other specimen is a fairly normal serpentine (Porthallow type). It consists chiefly of the peculiar orange-coloured granular serpentine (mineral), often much stained with hematite, the latter also occurring in minute rods, * See paper by Gen. MtMahon and myself, op. cit. pp. 471-475, and table of analyses (facing p. 466). 38 PROF, T. G. BONNEY ON THE [ Feb. 1896, and of small elongated prisms of colourless hornblende. It contains, however, a number of small ‘ inclusions,’ consisting almost wholly of clustered ferrite, surrounded by a clear zone, not quite so broad as they, of actinolite; and two larger inclusions (?), much ferrite- stained, recall the structure of a fluxion-breccia. This part of the slice is separated from the grey band by a rather sharply defined border. The latter affords indications of a banded structure in the presence of ill-defined lines of brown hornblende-grains (not numerous), of felspar(?)-grains, and (chiefly) of a felted mass of flaky or acicular actinolite, with which probably a colourless chlorite is also associated. These specimens, with that from Pare Bean Cove described. above, lead me to the conclusion that their adjacent faces indicate the junction-surface of the two rocks, but that here also the outer part of the serpentine has been rendered impure by some superficial melting of the hornblende-schist.* The facts cited above, it may be worth while to repeat, seem to indicate that the brownness of the hornblende’® is one indication of contact-metamorphism, while a more extreme result of the latter is the production of a rather fibrous, somewhat minute actinolitic hornblende and of sundry flaky minerals (representing the aluminous constituents of the rock), probably light-coloured chlorite or mica. Here I may refer to a section which has been mentioned more than once in former papers,* namely, that exhibited in a low crag at the foot of the main cliffs, north of Kynance Cove. On each visit I have spent some time in studying it, without, however, feeling much more certain as to its exact interpretation. As described on the first occasion, serpentine occurs on either side, and in the cliff above, the craglet in question, which exhibits, apparently in vertical bands, “ (2) a mass of grey, rather sandy, ‘ hornblende- schist,’ about 8 feet thick, with apparently many thin lamine of red serpentine; (3) red serpentine, rather fissile in structure, 23 feet; (4) a dark brownish-grey rock with crystals rather resembling diallage, 2 feet; (5) red serpentine, 42 feet, divided by a thin [rather wedge-shaped] band of the schist, then bedded schist like (2), with the apparent layers of serpentine, for about 6 feet.” * 1 It may be well to remark that the serpentine of the Lizard is generally very uniform in structure, and only departs from this rule (and that by no ene always) in the immediate neighbourhood of a junction with hornblende- schist. 2 I have more than once called attention to the fact that in hornblende a brown colour often precedes the green ; the latter may indicate an early stage in the process of hydration, affecting the ultra-microscopic grains of iron oxide or some constituent to which the colour is due. 5 Quart. Journ. Geol. Soc. vol. xxxiii. (1877) pp. 888, 920; vol. xxxix. (1883) p. 28. 4 «Rather more than 7 feet’ was my note in 1894; the measurements then were a little more precise than on former occasions, but the differences are 80 slight that I leave the passage as it stands. Between the last-named ‘schist’ and the serpentine (5) is a thin darkish dyke, which I had supposed to be part of the schist, and there may be another in the latter. Wol. 52.] ROCKS OF THE LIZARD DISTRICT. 39 Afterwards I described the microscopic structure of the rocks, pointing out that the serpentine is an unusually compact variety, and stating that I regarded the mass as representing a block of horn- blende-schist, caught up by the serpentine, altered thereby, and probably since then further changed by the action of water. In ‘the 18 years which have elapsed since I wrote these descriptions, my experience has been considerably enlarged, yet I still find the rock numbered (4) a very perplexing affair. I note that it is sporadically porphyritic, that the larger crystals under the micro- scope appear to exhibit traces of ‘ lustre-mottling,’ that the wedge-shaped piece included in the serpentine (5) is almost certainly a more compact variety of the same rock, and that this may have been a picrite ; also that the serpentine is probably the intruder. But I can now throw a little light on the banded structures, which are among the perplexities of the section. On examining the dyke-like serpentine (3) I found that towards the edges it gradually became banded. This structure on the right- hand side began to be indicated about 2 inches from the exterior, but only became very marked in the outer inch, where a grey tint predominated. The red part, on microscopic examination, is found to owe its colour to hematite-staining, and to consist of a serpentine (mineral) thickly crowded with minute flakes of a clear mineral, many of which give oblique extinction, and resemble actino- lite, but others give straight extinction, being probably a chlorite. The last inch, however, is practically colourless (only spotted with a few grains of iron oxide), consisting of matted flakes, quite double the length of those in the other part, but the same minerals. The edge of the serpentine (5), where it is in contact with the small dyke, exhibits a band about } inch wide. The red part resembles that described above, except that it seems to be a rather purer serpentine, and it contains one or two ill-preserved grains of bastite, while the band itself consists of a streak of fairly clear orange-coloured serpentine, followed by the matted minerals just mentioned, in which a kind of bandlet is formed by some small grains of brown hornblende, with a little streaking of serpentine. I have also examined a piece of the dyke, which is in contact with this face of the serpentine. Probably it was once a basalt; it has consisted mainly of two minerals, each of which has been replaced by secondary microliths: the clearer patches probably representing a felspar, the others almost certainly a pyroxene. But attached to this is a zone, which in the field I thought might represent a junction. This bears a considerable resemblance to part of the border in the other specimen, for it consists of a matted mass of acicular minerals, some being considerably larger than the rest and distinctly actinolitic, in which one or two grains suggest the possibility of having been bastite. Besides these I have examined ‘a piece of the striped red-and-grey rock (the supposed schist) in the left-hand part of the crag, where the bands locally are sharply folded. The red rock is a serpentine, like that already described ; the grey one is a mass of microliths, generally too minute for iden- 40 PROF. T. G. BONNEY ON THE [Feb. 1896, tification, but here and there in it are zones of larger flakes, in part: at least actinolitic, spotted with grains of hematite and of a pyroxene, in some cases certainly hornblende. Whether the whole of these two masses, which I formerly supposed to be mainly altered and decomposing hornblende-schists,. consists of serpentine streaked with bands, which are more nearly picrites in composition, it would be impossible to say without another and yet more minute examination, and this, perhaps, after all would hardly repay one for the trouble ; for it is now clear that: this section affords a conspicuous instance of a banding in the serpentine itself. As to the two larger, apparently included, masses. of ‘ brownish-grey ’ rock, I incline to regard them as pieces of a picrite, rather than as exceptionally altered fragments of the horn- blende-schist, but in the present state of my knowledge cannot: venture to speak more positively. V. CoNncLuUsIoNs. I submit, then, that the facts described in this paper justify the following conclusions :— (a) Mechanical forces, due to earth-movements, have only rather locally produced important effects on the crystalline rocks of the Lizard: namely, in a very limited area at Porthallow, near the great boundary-fault, and over a larger one in the south, approxi- mately bounded by a line drawn from a little east of Polpeor to rather south of Caerthillian Cove.’ (6) Elsewhere the results of such forces are of very secondary importance, being restricted to the neighbourhood of faults, and even there producing commonly very limited effects. (c) The slightly foliated or linear structure rather common in the serpentine, its occasional distinct banding, together with rather similar structures in the gabbro and a faint approach to them in certain basic dykes, as has been more fully shown in the paper by General M*Mahon and myself, have nothing to do with ‘ dynamo- metamorphism, but have been produced by fluxion-movements anterior to the complete consolidation of the rock. (ad) The serpentine is intrusive in the ‘ granulitic group,’ which, however (though it may have torn off large blocks), it has only locally softened and indented. It is also intrusive in the hornblende-schist, but this it has sometimes riven, and occasionally melted down, in certain cases partially, in others perhaps wholly, thus producing the streaks of a less pure character, with some resemblance to the former rock: these phenomena, as might be expected, being restricted to the exterior of the mass, the rest of it generally exhibiting an uniform character for considerable distances. In short, though the effect of twelve years’ work in the field and with the microscope has caused me to change my views as to the 1 An area very nearly correspondent with that assigned to the ‘mica-slate series’ of Sir H. De la Beche. The line, if it runs straight (I have not attempted to trace it), would be roughly from N.W. to S.E. Vol. 52.] ROCKS OF THE LIZARD DISTRICT. 41 genesis of the ‘granulitic group’ and the hornblende-schists, I adhere (except in regard to a few matters of detail) to the conclusions which were expressed in my paper published in 1877, and more emphatically than ever to those expressed in the first three of the above paragraphs—namely, that I can find no ground for attributing the foliated or banded structures, whether in the granulitic and the hornblendic groups or in the serpentine, gabbro, and a few basic dykes, to dynamo-metamorphism. As regards the banding of the granulitic and hornblendic rocks, I can only say that if it be due to any kind of shearing in solid heterogeneous materials—it is not easy to follow mentally the steps of the process—recrystallization has been so complete that the usual indications of such action have vanished. Hence the structure must have been produced anterior to the incoming of the serpentine and the gabbro. Yet, if the serpentine were folded together with the granulitic rock so as to distort its bands, traces of crushing and shearing should be found in the latter. Even if we assume these to have disappeared (which I could not admit) and claim the foliated and banded structure occasionally exhibited by the gabbro as a result of dynamo-metamorphism, what is the testimony of the serpentine? It is sometimes welded to the granulite, often to the hornblende-schist ; it is constantly cut intrusively (every- body, I believe, grants this) by dykes or veins of gabbro. But the serpentine almost invariably shows no signs of crushing. Strain and pressure might destroy a weld, but I never knew them produce one between rocks of this kind; hence the foliation and banding of the serpentine cannot be due to any such cause.’ - But serpentine is a much more brittle rock than granite, horn~- blende-schist, or gabbro; the last, as one quickly learns in the Alps, being a very obdurate material. Hence earth-movements, which would affect these rocks, would leave their marks distinctly enough on the serpentine. This is a brief summary of my observations in regard toit. Under strain, perhaps under moderate pressure, serpen- tine simply brecciates*; when the pressure becomes more severe the rock breaks into pieces, which are generally rather lenticular in shape, with a ‘glaze’ on the outside,’ and, as a final stage of the ‘peine forte et dure,’ the serpentine becomes so slaty that it might be sometimes used for roofing purposes.* The Alps afford many 1 On this point I am not afraid of being accused of speaking dogmatically. My first visit to the Lizard was in the autumn of 1873, and I speedily fell a victim to the fascinations of serpentine, probably because I found it to bea subject where quot homines tot sententie held good. I have never felt strongly attracted to beaten paths. Since then I have studied serpentine (including peridotite) in the field on an average once ina year. I have returned five times to the Lizard, I have been thrice to Anglesey, I have examined the rock in three districts in Scotland, in at least a dozen separate localities in the Alps (in some cases not only as a passing traveller), in two districts of the Apennines, and in the Pyrenees, besides studying with the microscope specimens collected expressly by myself, with many others acquired by gift or by purchase. The effects of earth-movements also are not novel to me, since for more than a dozen years I have been studying these in the Alps and elsewhere. ? Geol. Mag. 1879, p. 365. 3 Ibid. 1880, p. 588, and elsewhere. 4 Ibid, 1890, p. 533. AQ PROF. T. G. BONNEY ON THE [ Feb. 1896; opportunities of studying these changes. Towards the outside of a large mass, in a region which has undergone severe pressure, one may find the ‘lenticular’ structure, and it is vain to hope for a decent specimen, but as we pass inward the rock often becomes less | brecciated, so that at last fairly normal specimens may be obtained. Even the slaty structure may not affect the whole of a large mass ; now and again portions of it escape comparatively uninjured. Of this, however, we may be sure, that if a force had acted sufficient to produce a marked effect on either the granulite, the hornblende- schist, or the gabbro, the serpentine would have been almost invari- ably torn apart from the weld, and would have been crushed, perhaps to a slate, for at least a considerable distance from the junction.’ If, then, the relations of the serpentine with the granulites and the hornblende-schists indicate an ‘ igneous complex,’ if its structures and those of the gabbro are the results of dynamo-metamorphic action on the rocks when they were solid, the Lizard district flatly contradicts everything which I have learnt about rock-struc- tures during more than twenty years of work in the field and of studying under the microscope specimens collected with my own hands. VI. APPENDIX. (a) Miscellaneous Notes. It would be a very long task to examine every rock in such a . district as the Lizard, so that even in going over ground compara- tively familiar one picks up ‘crumbs’ of information, some of which may. be worth a brief record. Dykes.—A porphyritic diabase, as described by Messrs. Fox and Teall, and by Gen. M°Mahon and myself, is occasionally found, usually in rather thin dykes. Those hitherto recorded, if not actually confined to the hornblende-schist, are closely associated with it, as near Potstone Point,” but we came upon one cutting through ser- pentine (the variety with small crystals of colourless hornblende) near the path* leading from Mullion Village to Predannack Wartha. The hornblende-schist, near the western end of the cliffs on the northern side of Porthoustock Cove, is cut obliquely by a yel- lowish rock, generally rather decomposed, which, though only a few inches thick, is more like a dyke than an infiltration-vein. I find this on microscopic examination to exhibit a finely granular struc- ture not resembling any of those usual in veins, and to consist of epidote. This mineral no doubt readily forms as a secondary product in rocks of suitable composition, but the uniformity in composition is a little strange. Such an epidosite would come most readily from arock composed of a lime-felspar with some minutely 1 The effects of pressure are never more conspicuous than in the weaker of two rocks near the junction-surface. y 212, 3) 3 It is about 350 yards, in a line drawn rather N. of E., from Oreggian ‘Mill; in the same direction are two other shallow pits in serpentine. Vol. 52.] ROCKS OF THE LIZARD DISTRICT. 43 disseminated iron oxide. Two or three dykes of coarse gabbro, very poor in the ferro-magnesian silicates, have indeed been observed on the coast farther south; can this epidosite have been a very compact variety of the same rock? Manacle Point and Porthoustock Cove-—We can add a few notes to the description given by Gen. M*Mahon and myself... The ordinary gabbro (which forms the Crousa Down massif) when followed along the shore towards Manacle Point, passes occasionally into a very coarse variety, in which the constituent crystals some- times even exceed 2 inches in length. This forms patches in the ordinary rock, with ill-defined boundaries, suggestive of an imperfect mixture of heterogeneous materials in different stages of consolida- tion. Other parts of the gabbro are foliated, and these occur in like manner, so as to suggest local movements anterior to complete consolidation. The ‘warm grey’ or brownish rock intrusive in the gabbro,” especially as Manacle Point is approached, would repay a closer study than our arrangements allowed us to give it. It pierces and rips up the ordinary gabbro in a very curious fashion, and pieces of the latter sometimes assume singular shapes, as if they had been slightly softened and bent (fig. 11). Frequently, also, it Fig. 11.—Strip of moderately coarse gabbro included in granular dolerite (or gabbro), south of Porthoustock Point. The unmarked part indicates the latter rock. The sketch is diagrammatic. The inclusion represented measures nearly 2 feet from end to end. includes flake-like fragments of the foliated variety.? Besides this, it rather often exhibits a porphyritic structure, the mineral being commonly felspar, but sometimes a variety of pyroxene, which forms green spots. The felspar-crystals are a dead-white colour, like that in the gabbro, ranging up to about half-an-inch in length. They are ‘ sporadic’ in habit, occurring in small ‘ swarms,’ some- times more or less scattered. Sometimes, also, they are actually in contact, and it becomes difficult to distinguish them from the smaller rock-fragments. Occasionally a felspar, as it appears at first, proves on examination to contain a speck of diallage. In short, the * Quart. Journ. Geol. Soc. vol. xlvii. (1891) p. 491. * It is noticed on pp. 491 and 494 in the paper by Gen. MeMahon and myself. As there stated, it is a kind of dolerite or fine-grained gabbro. * The bearing of these observations on some of the reasoning in the earlier part of this paper will, I presume, be obvious. 44 PROF. T. G. BONNEY ON THE [Feb. 1896, intrusive finer-grained rock seems to have softened, bent or drawn out some fragments of the coarser gabbro, and even to have partly melted down others, destroying the pyroxenic rather than the felspathic constituents, so that the latter are scattered sporadically in the newer rock.’ Prof. Sollas, it will be remembered, has described a somewhat similar occurrence in the Carlingford district.” This intrusive rock is less abundant than the ordinary gabbro, but more so than the ‘ greenstone’ * dykes, which cut them both, and usually do not exceed 4 or 5 feet in thickness. A low spring tide enabled us to make a more complete examina- tion of the southern side of Porthoustock Cove. As mentioned in our paper (p. 491), General M*Mahon and myself felt uncertain as to the nature of the rocks forming the shore and adjacent cliffs. They presented, as we remarked, some resemblance to the more dioritic members of the ‘granulitic group,’ and were cut by ‘ greenstone’ dykes, like those mentioned above, the gabbro being near at hand; for we traced it on the slopes above the cliff almost to the head of the cove.* This time we managed to get along the shore eastward, to a point where the ordinary gabbro was exposed in the face of the cliff. Here the rocks on which we stood consisted beyond question of the fine-grained gabbro or dolerite, becoming, as usual, sporadic- ally porphyritic in the neighbourhood of the coarser rock, and from this point we succeeded in following it westward, and convincing ourselves that, though somewhat disguised by the effects of faulting and weathering, it is the dominant rock on this side of the cove. It is cut, as has been said, by ‘ greenstone’ dykes, and traversed. not unfrequently by reddish veins. Some of these appeared due vo infiltration, but others resembled a rather felspathic gabbro, by no means identical with that forming the principal massif. Thus Porthoustock Cove marks the position of a fault or group of faults,’ which brings together the Crousa Down gabbro, with its associated inirusives, and the hornblende-schist. Serpentine.— We examined the mass at Porthkerris ° more care- fully than on former occasions. It is represented in the geological 1 Microscopic examination. confirms the statements made above, and discloses one or two other facts of general interest. In the granular ground- mass the felspars are generally fairly well preserved ; the pyroxenic constituent was originally an augite, very pale brown in thin sections, which now, without change of external form, is replaced by a brown, strongly pleochroic hornblende (brownish straw-colour to rich brown). The felspar of the included fragments is almost wholly replaced by secondary and mostly earthy material ; the augite by fibrous, often felted, aggregates of a greenish actinolitic hornblende. Here and there the included fragments are so minute that one can hardly identify them with certainty. ? Trans. Roy. Irish Acad. vol. xxx. (1894) p. 477. The changes, however, in this instance are different—probably owing to local cireumstances—from those observed by him. 3 I use this vague term designedly, for they may be anything from a fine- grained dolerite or basalt to a hornblendic diabase. 4 Still cut by the fine-grained gabbro or dolerite and by the ‘ greenstone.’ ° The coves in the Lizard almost invariably correspond with one or more dislocations. 6 Polkerris in earlier papers. In this I have followed the nomenclature of — the 6-inch Ordnance map. Vol. 52. ] ROCKS OF THE LIZARD DISTRICT, 45 map as coming down to the shore on the northern side of the cove; but if there be an outcrop here, it was concealed on this occasion. At any rate, I think it must be isolated from the main mass of the serpentine; this crops out in many places on the moorland which rises on the northern side of the little valley, being seen over an area measuring about 200 yards from east to west, and not more than this in a transverse direction, hornblende-schist cropping out south, east, and north of it. Whether this mass of serpentine is continuous with the one at Porthallow we could not determine, the two being separated by rather more than a furlong of covered ground. Macroscopically it agrees fairly well with one variety of that rock, but it is perhaps a little smoother in aspect and brighter in colour. It has been much cracked and then cemented by yellowish steatite, so that it is apt to break up under the hammer. The two rocks agree fairly well in microscopic structure, each resulting from the alteration of a fine-grained peridotite, which appears to have consisted simply of olivine and iron oxide (7. ¢. a kind of dunite).’ We ascertained that at Porthallow the serpentine not only runs up the cliff in a dyke-like fashion, but also does this at each end, so that the shape of the mass might be compared—very roughly—to a flattish crescent with its back to the water.” The quarry afforded better sections than it had done for some years. I can understand doubts arising about the interpretation of particular sections, but not as to the general fact that the serpentine is intrusive in the hornblende-schist. We again paid much attention to the structure in the serpentine resembling a foliation, which may be observed in many places, more distinctly on the western than on the eastern coast, though on the latter also, as from Kildown Point to Kennack Cove, it is often to be found. Frequently it is barely perceptible on a perfectly fresh face of the rock, becomes visible on wave-worn surfaces, and is quite distinct on weathered crags. It obviously proceeds from a slight alignment of the constituents in the original peridotite, and in the case of bastite-serpentine seems more especially determined by that mineral. While it is not seldom fairly persistent in orientation over considerable areas, marked changes in direction may be observed; and while in the neighbourhood of included masses of granulite it is sometimes parallel with the junction-surfaces, cases not unfrequently occur where it makes a high angle with them. In other words, we have failed to discover any necessary relation between the structures in the two rocks. The serpentines in which this ‘foliation’ exists do not exhibit, macroscopically or micro- scopically, any indications of strain or crushing, and I adhere to the opinion expressed by Gen. M°Mahon and myself,* that the structure was produced while the original peridotite was consolidating. 1 [refer to the ordinary serpentine of Porthallow, regarding the banded variety as exceptional, 2 The slopes here are steep, rough, and much overgrown with brambles and coarse herbage, so that it is not easy to map the outcrops, and we have not attempted to do this very precisely. 3 Quart. Journ. Geol. Soc. vol. xlvii. (1891) pp. 447, 476. 46 PROF. T. G. BONNEY ON THE [Feb. 1896, We have already pointed out’ that the Lizard affords two fairly distinct types of serpentine — one, that more generally known, containing distinct. grains of bastite (¢. g. Kennack Cove), and sometimes augite in addition (¢. g. Coverack Cove); the other, in which the bastite, if present, is inconspicuous, while small crystals of white hornblende are abundant (¢. g. south of Mullion Cove); the former being most abundant on the eastern, the latter on the western coast.” But we find the bastite-serpentine on the west coast to the south of Kynance Cove,’ and again on the actual headland of the Rill. Here, also, within a short distance, the peculiar variety of serpentine occurs which has been said to contain felspar,* but I could not discover how they were related. From north of Kynance to Gue Graze the dominant serpentine is a rather compact, slightly streaked rock, which on the whole seems more nearly related to the hornblendic than to the bastite-serpentine. The hornblendic ser- pentine also occurs, though not abundantly, on the east coast ; that at Porthallow ° on the whole more nearly agrees with it than with the other ; we find it on the shore for some little distance south of Poltesco Cove and from Cadgwith to Carnbarrow. But the most curious instance is at Kildown Point. In the quarry at the top we find the bastite-serpentine, while the mass at the foot of the cliff ® is a very typical hornblende-serpentine. I regret that I have not from the first recorded the variety of serpentine in each quarry or outcrop examined; but, so far as I remember or have noticed, the serpentine, at places within a curved line drawn from Coverack to Kynance Cove, roughly symmetrical with the eastern coast, is generally the bastite variety, and that outside this line is the horn- blendic variety, including with it the dull compact type already mentioned. . Green Schists of the Southern Coast.—We paid special attention to the relations of these schists with the normal hornblende-schists, and are more than ever satisfied that, as stated by Gen. M°Mahon and myself, they are only the latter rocks modified by extreme pressure.” In more than one place we were able to trace a gradual 1 Quart. Journ. Geol. Soc. vol. xxxix. (1883) p. 23, and vol. xlvii. (1891) pp- 466-468. 2 Sp. gr. (mean) of four specimens of the former (two determined for this paper) soe Sp. gr. of three specimens of the latter (two determined for this aper) 2°755. E P