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THE
QUARTERLY JOURNAL
GEOLOGICAL SOCIETY OF LONDON.
EDITED BY
THE ASSISTANT-SECRETARY OE THE GEOLOGICAL SOCIETY.
Quod si cui mortalium cordi et curae sit non tantura inventis heerere, atque iis uti, sed ad ulteriora 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) aeadjungant, —Novum Organum, Prce/atio.
VOLUME THE THIRTY-NK^i^
,883' "aSH^U?
LONDON : LONGMANS, GREEN, READER, AND DYER.
PARIS! FRIED. KLINCKSIECK, 11 RUE DE LILLE; P. SAVY, 24 RUE HAUTEFEUILLE. LEIPZIG: T. O.WEIGEL.
SOLD ALSO AT THE APARTMENTS OP THE SOCIETY, MDCCCLXXX1II.
test
OFFICERS
GEOLOGICAL SOCIETY OF LONDON,
Elected February 16, 1883.
$resifotnt*
J. W. Hulke, Esq., F.R.S.
^t«*8wtffo«itt.
Prof. P. M. Duncan, M.B., F.R.S. R. Etheridge, Esq., F.R.S.
J. Gwyn Jeffreys, Esq., LL.D., F.R.S. Prof. J. Prestwich, M.A.,F.R.S.
§mttavit#.
Prof. T. G. Eonney, M.A., F.R.S. | Prof. J. W. Judd, F.R.S.
Warington W. Smyth, Esq., M.A., F.R.S.
Creagurm
Prof. T. Wiltshire, M.A., F.L.S.
©©TO^DL-
H. Bauerman, Esq.
W. T. Blanford, Esq., F.R.S.
Prof. T. G. Bonney, M.A., F.R.S.
W. Carruthers, Esq., F.R.S.
Prof. P. M. Duncan, M.B., F.R.S.
R. Etheridge, Esq., F.R.S.
John Evans, Esq., D.C.L., LL.D., F.R.S.
A. Geikie, Esq., LL.D., F.R.S.
Rev. Edwin Hill, M.A.
G. J. Hinde, Esq., Ph.D.
Prof. T. M'Kenny Hughes, M.A.
J. W. Hulke, Esq., F.R.S.
J. Gwyn Jeffrevs, Esq., LL.D., F.R.S.
Prof. T. Rupert Jones, F.R.S.
Prof. J. W. Judd, F.R.S.
S. R. Pattison, Esq.
J. A. Phillips, Esq., F.R.S.
Prof. J. Prestwich, M.A., F.R.S.
F. W. Rudler, Esq.
Prof. H. G. Seeley, F.R.S., F.L.S.
Warington W. Smyth, Esq., M.A., F.R.S.
W. Topley, Esq.
Prof. T. Wiltshire, M.A., F.L.S.
?ig$fetant*J^cretarj), HtBrartan, antf Curator.
W. S. Dallas, Esq., F.L.S.
Cterfc.
Mr. W. W. Leighton.
fitbrarp antf flSLuttum tetetaut.
Mr. W. Rupert Jones.
T1BLE OF CONTENTS.
Page
Bonney, Prof. T. G. The Hornblendic and other Schists of the Lizard District, with some Additional Notes on the Serpentine. (Plate I.) 1
. Notes on the Lithological Characters of some Rocks
from Ross and Inverness Shires 159
. Additional Notes on Boulders of Hornblende-Picrite near
the Western Coast of Anglesey , 254
. Notes on a Series of Rocks from the North-west Highlands,
collected by C. Callaway, Esq 414
. On a Section recently exposed in Baron-Hill Park, near
Beaumaris 470
On the Rocks between the Quartz-felsite and the Cambrian
Series in the Neighbourhood of Bangor 478
Callaway, Dr. C. The Age of the Newer Gneissic Rocks of the Northern Highlands. — With Notes on the Lithology, by Prof. T. G. Bonney 355
Claypole, Prof. E. W. On Helicopora. a new Spiral Genus (with
three species) of North- American Fenestellids. (Plate IV.) . . 30
David, J. W. Edgeworth, Esq. On the Evidence of Glacial
Action in South Brecknockshire and East Glamorganshire .... 39
Dawkins, Prof. W. Boyd. On the Alleged Existence of Ovibos moschatus in the Forest-bed, and on its Range in Space and Time 575
Diller, J. S., Esq. Notes on the Geology of the Troad. A brief Summary of the Results derived from the Observations made in connexion with the Assos (U. S.) Expedition. With an Appendix by W. Topley, Esq 627
Gardner, J. S., Esq. On the Lower Eocene Section between Reculvers and Heme Bay, and on some Modifications in the Classification of the Lower London Tertiaries 197
Geikie, Archibald, Esq. On the supposed Precambrian Rocks of St. David's. (Plates VIII.-X.) 261
iv TABLE OF CONTENTS.
Page
Gray, Thomas, Esq. On Gray and Milne's Seismographic Apparatus 218
, and Prof. J. Milne on the Elasticity and Strength-constants
of Japanese Rocks 139
Hausler, Dr. R. Notes on some Upper Jurassic Astrorhizidse and Lituolidae. (Plates II. & III.) 25
Hicks, Dr. H. On the Metaniorphic and Overlying Pocks in parts of Ross and Inverness Shires. With notes^on the Microscopic Structure of some of the Rocks, by Prof. T. G. Bonney. (Plate
vi.) ..: ui
Hudleston, W. H., Esq. Notes on a Collection of Fossils and of Rock-specimens from West Australia., north of the Gascoyne River. (Plate XXIIL) . . . 582
Irving, Rev. A. On the Mechanics of Glaciers, with especial
Reference to their supposed Power of Excavation 62
. On the Origin of Valley-Lakes, with especial Reference
to the Lakes of the Northern Alps 73
Judd, Prof. J. W. On the Basalt-glass (Tachylyte) of the Western
Isles of Scotland. (Plates XIII. & XIV.) 444
Jukes-Browne, A. J., Esq. On the Relative Ages of certain
River-valleys in Lincolnshire 506
Keeping, H., Esq., and E. B. Tawney, Esq. On the Section at Hordwell Cliffs from the top of the Lower Headon to the base of the Upper Bagshot Sands 566
Milne, Prof. J., and T. Gray, Esq. On the Elasticity and Strength- constants of Japanese Rocks „ 139
Monckton, H. W., Esq. The Bagshot Beds of the London Basin . 348
Owen, Prof. R. On Generic Characters in the Order Sauropterygia. 133
. On the Skull of Megalosaurus. (Plate XI.) 334
Reade, T. Mellard, Esq. The Drift-beds of the North-west of England and North Wales. Part II. Their Nature, Stratigraphy, and Distribution. (Plate V.) 83
Seeley, Prof. H. G. On the Dorsal Region of the Vertebral Column of a new Dinosaur (indicating a new genus, Sphenospondylus) from the Wealden of Brook in the Isle of Wight 55
. . On the Dinosaurs from the Maastricht Beds 246
Sollas, Prof. W. J. Descriptions of Fossil Sponges from the In- ferior Oolite, with a Notice of some from the Great Oolite (Plates XX. & XXI.) 541
. The Estuaries of the Severn and its Tributaries ; an in- quiry into the nature and origin of their tidal sediment and alluvial flats 611
Tawney, E. B., Esq., and H. Keeping, Esq. On the Section at Hordwell Cliffs from the top of the Lower Headon to the base of the Upper Bagshot Sands 566
TABLE OF CONTENTS. v
Page
Tomes, R. F., Esq. On the Fossil Madreporaria of the Great Oolite
of the counties of Gloucester and Oxford. (Plate VII.) 168
. On some new or imperfectly known Madreporaria, from
the Coral Rag and Portland Oolite of the counties of Wilts, Oxford, Cambridge, and York. (Plate XXII.) 555
Topley, W., Esq. Appendix to Mr. J. S. Diller's "Notes on the
Geology of the Troad." 633
Walford, Edwin A., Esq. On the Relation of the so-called " North- ampton Sand " of North Oxon to the Clypeus-grit 224
Waters, A. W., Esq. Fossil Chilostomatous Bryozoa from Muddy
Creek, Victoria, &c. (Plate XII.) 423
Wethered, E., Esq. On the Lower Carboniferous Rocks of the
Forest of Dean, as represented in typical sections at Drybrook . 211
borne, Rev. G. F. Notes on some Fossils, chiefly Mollusca, from the Inferior Oolite. (Plates XV.-XIX.) 487
Woodward, C. J., Esq. On a group of Minerals from Lilleshall,
Salop 466
PROCEEDINGS.
Annual Report 8
List of Foreign Members 16
List of Foreign Correspondents 17
List of Wollaston Medallists 18
List of Murchison Medallists 19
List of Lyell Medallists 20
List of Bigsby Medallists 21
Applications of the Barlow-Jameson Fund 21
Financial Report "
Award of the Medals &c 29
Anniversary Address 3 8
Donations to the Library (with Bibliography) 77
Goppert, Prof. H. R. On Vegetable Remains in Amber 66
Mackintosh, D., Esq. Results of Observations in 1882 on the posi- tions of Boulders relatively to the Underlying and Surrounding
vi TABLE OF CONTENTS.
Page
Ground in North Wales and North-west Yorkshire ; with remarks on the evidence they furnish of the recency of the close of the Glacial Period 67
Oats, Fbancis, Esq. On Mr. Dunn's " Notes on the Diamond Fields
of South Africa, 1880" 5.
Peyton, John E. H., Esq. On a Wealden Fern, Oleandridium (Tcs-
niopteris) Beyrichii, Schenk, new to Britain 3
Vine, G. R., Esq. Notes on the Corals and Bryozoans of the Wen- luck Shales (Mr. Maw's washings) 69
LIST OF THE FOSSILS FIGURED AND DESCRIBED 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.
Plants.
Oleandridium (Taeniopteris) Bey- I richii Wealden
Hastings
Amorphozoa.
Calathiscus variolatus. PI. xxi. f. ^
17-20
Emploca ovata. PL xx. f. 1-6
Leptophragma fragile. PL xx. f. 10,
11
Limnorea pygrncea. PL xxi. f. 29, 30 Mastodictyum Whidborni. PL xx.
f. 7-9
Myrmecium depressum
Peronella Metabronnii. PL xxi.
f. 26, 27
repens. PL xxi. f. 31
Platychonia elegans. PL xxi. f. 22-25 Plectospyris elegans. PL xx. f. 12-14
major. PL xx. f. 15, 16
Thaumonema pisiforme. PL xxi.
f. 28
Inferior Oolite .
Great Oolite .
Inferior Oolite. Great Oolite .
Inferior Oolite. Great Oolite .
Inferior Oolite.
Great Oolite
England
England
England England
England England
England England
546 542
545
549
544
550
548 548 547 545 546
549
Rhizopoda.
Hyperammina vagans. Placopsilina cenomana. Psammosphaera fusca.
PL ii. f. 2-6 ^ PL iii. f. 1 PLii. f. 1..
Reophax helvetica. PL ii. f. 8-10...
multilocularis
scorpiurus. PL ii. f. 7 ....
Thurarnmina heraisphaerica. PL iii.
f. 7-9
papillata. PL iii. f. 2-6
Upper Jurassic.
Switzerland,
26 27 26 27 26 27 28
27
TOSSILS FIGURED AND DESCRIBED.
Name of Species.
Formation.
Locality.
Page
CoELENTERATA.
{Actinozoa.)
Amplexus pustulosus. PI. xxiii. f. 1
Anabacia complanata
Astroccenia major. PI. xxii. f. 5, 16
Phillipsi. PI . vii . f . 6 , 7
Bathyccenia Slatteri. PI. vii. f. 1, 8
solida. PI. vii. f. 9, 10
Chorisastrsea obtusa
Confusastraea burgundiae
magnified. PI. vii. f. 15, 22...
Crateroseris fungiformis. PL xxii.
f. 11-14
Cryptocaznia mierophylla. PI. vii. ~\
f. 2 I
Cyatbophora Bourgueti. PI. vii. j
f. 3, 4 J
Dimorpharcea, sp
Enallohelia clavata. PI. vii. f. 12-14 ^ Favia pedunculata. PI. vii. f. 16, 1 7 |
Isastraea explanulata }
gibbosa |
limitata J
oblonga. PL xxii. f. 6
Latimaeandraraea corallina 1
■ decor -ata. PL xxii. f. 7-10, 15 J
Microsolena excelsa ]
Montlivaltia caryophyllata. PL vii. \
f. 11 J
fairfordensis. PL vii. f. 21... "j
Slatteri. PL vii. f. 20 I
Oroseris Slatteri. PL vii. f. 5 |
Stylina solida J
Thamnastraea arachnoides 1
concinna. PL xxii. f. 1-4 J
Lyelli "|
mammosa I
mierophylla j
Waltoni J
Thecosmilia Slatteri 1
Tricycloseris Umax. PL vii. f. 18, 19 J
Carboniferous Great Oolite Coral Rag ...
Great Oolite
Coral Rag
Portland Oolite- Coral Rag ... |
Great Oolite . . .
Great Oolite ...
Coral Rag
Great Oolite ... Great Oolite ...
W. Australia ..
England
England
Oxfordshire
Gloucestershire .
Oxfordshire
Gloucestershire.
England
Oxfordshire
Steeple Ashton .
Gloucestershire.
England
Upware
Oxfordshire
Oxfordshire
England
Gloucestershire . Gloucestershire.
England
Highworth
Malton
England
591 193 557 188 176 177 186 184 184
560
179
194 561 175 183 186 185 185 563 562 562 190
180 181 181 192 180 558 559 188 190 188 189 182 191
ECHINODERMATA.
Chirodota convexa. PL xix. f. 14...
gracillima. PL xix. f. 15
Rhabdocidaris Thurmanni, var. re- gens. PL xix. f. 13
Inferior Oolite.
England.
537 537 536
FOSSILS FIGURED AND DESCRIBED.
IX
Name of Species.
Formation.
Locality.
Page.
POLYZOA.
Tertiary
Carboniferous
Carboniferous .
Upper Silurian. Devonian
Catenicella alata. PI. xii. f. 15, 16.. ")
ampla
circumcincta
Harveyi. PI. xii. f. 5
hastata
internodia, var. august ata
laevigata. PI. xii. f. 1
longicollis. PI. xii. f. 2-4
taurina
ventricosa )
Evactinopora crucialis. PI. xxiii. ]
f-2
dendroidea. PI. xxiii. f . 3 ... J
Helicopora archimediformis. PI. iv. 1
f-3,4 I
latispiralis. PI. iv. f. 1 , . . .
Ulrichi. PI. iv. f. 2
Lunulites initio,. PI. xii. f. 8
petaloides. PI. xii. f. 11
Membranipora arethusa. PI. xii.
f. 19
lusoria, var. coarctata. PL
xii. f. 20
macrostoma
oculata. PI. xii. f. 22
roborata
Membraniporella nitida
Micropora cavata
ordinata
Microporella cellulosa
symmetrica )■
Monoporella sexangularis
Porella marsupium
Retepora Beaniana
marsupiata, var. mucronatd ..
Schizoporella australis |
schizostoma
Selenaria maculata. PL xii. f. 7, 9
12
parvicella
punctata
Smittia collaris. PI. xii. f. 10
Napierii. PI. xii. f. 14
turrita )
Stenopora tasmaniensis Carboniferous
Australia
W. Australia
U.
America
Tertiary
Australia
W. Australia
428 429 432 431 431 430 432 432 431 431
593 594
34
32
33
442
442
434
434 433 434 433 436 435 435 43/ 436 435 437 439 439 439 439
440 441
440 438 438 438 592
MOLLUSCA.
( Palliobranchiata.) Terebratula Tawneyi. PI. xix. f. 12. (Inferior Oolite.
Dundrv i 536
FOSSILS FIGURED AND DESCRIBED.
Name of Species.
Formation.
Locality.
Page.
Mollusca (continued). (Lamellibranchiata.)
Area aiquata cf. ^
culmotecta. PL xviii. f. 1 ...
As t arte anatiformis. PL xviii. f. 14
elegans, var. munda. PI. xix.
f. 4
magnalis
sufflata. PI. xviii. f. 15, 16 ...
Cardium dundriense. PL xviii. f. 8.
pulsatum. PL xviii. f. 9
Cypricardiafiloperta. Pl.xviii. f. 19. Exogyra Davidsoni. PL xv. f. 10...
globulus. PL xv. f. 11
Gervidia gladiolus. PL x vi. f. 7
intermedia. PL xvi. f. 8, 9 ...
compressa. PL xvi. f . 6
Gouldia ovalis. PL xviii. f. 17
mitralis. PL xviii. f. 18
Gryphaa abrupta. PL xv. f. 7
cygnoides. PL xv. f. 8
cvmbium
S&llasii. PL xv. f. 9
Harpax Parkinsoni. PI. xv. f. 20...
Tawneyi. PL xv. f. 18, 19 ...
Hinnites tenuistriatus
Isoarca capitalis. PL xviii. f . 6 ...
texata. PL xviii. f . 7
Kellia Etheridgii. PL xviii. f. 12, 13
Lima alticosta
amnifera. PL xvii. f . 2
contorquens. PL xvii. f . 3 ...
cubiferens
educta. PL xvii. f. 4
incisa |
inoceramoides. PL xvii. f. 5 .
laeviuscula
Lycettii
majestica. PL xvii. f . 6
notata
cepybolus. PL xvii. f . 1
placida. PL xvii. i.7
platybolus. PL xvii. f. 8
poetica. PL xvii. f. 9
rigida
rodburgensis. PL xvii. f. 10...
semicircularis
seminuda. PL xvii. f. 11
Sharpii. PL xvii. f. 12
strigillata
Lucina burtonensis
Macrodon rapidus. PL xviii. f. 2, 3
rasilis |
Myacites subsidens. PL xviii. f. 24 J
Inferior Oolite.
England
FOSSILS FIGURED A*TD DESCRIBED.
Name of Species.
Formation.
Locality. I Page.
Mollusca (continued). Lamellibranchiata (continued).
Myoconcha implana. PL xviii. f. 22, ^
PL xix. f. 5
unguis. PL xviii f . 21
Mytilus primipilaris. PL xvi. f. 13
striatissimus. PL xvi. f. 12
Nucula sequilateralis
nuciformis. PL xviii. f . 5 ...
subglobosa. PL xviii. f . 4 ...
Opis spathulosus. PL xviii. f. 20...
Ostrea costata
explanata
Knorrii. PL xv. f. 2, 3
palmetta, var. montiformis ...
pyrus. PL xv. f. 4
spharoidalis. PL xv. f. 5, 6 .
Pecten aratus
cornutus. PL xvi. f. 1, 2 ...
demissus. PL xv. f. 15
fenestralis. PL xv. f . 12
gingensis
intermittens, PL xv. f. 13...
laeviradiatus
■ puellaris. PL xix. f. 3
spinicostatus. PL xv. f. 1 4 . . .
triformis. PL xvi. f . 3
Pholadomya bellula. PL xix. f. 10 .
callcea. PL xix. f. 7
fortis. PL xix. f. 8
Newtonii. PL xix. f . 9
spatiosa. PL xix. f. 11 -.
Pinna claviformis. PL xvi. f. 11...
dundriensis. PL xvi. f. 10...
Placuna Rupertina. PL xv. f. 16 . .
sagit talis. PL xv. f. 17
Plicatula Sollasii. PL xv. f. 21, 22
subserrata PL xvi. f. 4, 5 ...
Spbsera crassicosta. PL xvi. f. 16 .
fimbriata. PL xviii. f. 10, 11
Thracia leguminosa. PL xviii. f. 23 Studeri. PL xix. f. 6 J
Inferior Oolite . .
England
530 530 518 519 522 523 522 529 491 490 490 492 492 493 497 498 498 500 499 500 501 501 502 502 534 532 533 533 534 518 518 496 497 515 515 526 525 531 531
Ancyloceras Waltoni. Toxoceras Orbignyi.
(Cephalopoda.)
PL xix. f. 1 . PL xix. f. 2...
}l
Inferior Oolite... England
(I
488 488
Xll
FOSSILS FIGURED AND DESCRIBED.
|
Name of Species. |
Formation. |
Locality. |
Page. |
|
|
Vertebrata. |
||||
|
(Reptilia.) |
||||
|
Cretaceous Inferior Oolite... Cretaceous Wealdp.n |
Maestricht Dorsetshire Maestricht Isle of Wight ... |
246 |
||
|
Bucklandi. PL xi |
334 |
|||
|
248 |
||||
|
55 |
||||
|
(Mammalia.) |
||||
|
Ovibos moschatus |
|
Forest-bed ... |
Norfolk |
575 |
EXPLANATION OF THE PLATES.
Plate Pagb
Apparent Current-bedding in Lizard Rocks, to illustrate I. -j Prof. T. G. Bonney's paper on the Hornblendic and other
Schists of the Lizard district 24
■yj f Swiss Jurassic Foraminifera, to illustrate Dr. R. Hausler's ttt parser on some Upper Jurassic Astrorhizidae and Lituo- 1JX [ lidae 28
Ty f Helicopora, to illustrate Prof. E. W. Claypole's paper on
\ thatgenus 38
Map of the Basin of the Mersey and of part of the Dee, to V. \ illustrate Mr. T. Mellard Reade's paper on the Drift-beds
of the North-west of England and of North Wales 132
-{
Map of Parts of Ross- and Inverness-shires, to illustrate VI. -^ Dr. Hicks's paper on the Metainorphic and Overlying Rocks
of that district 166
| Great-Oolite Corals, to illustrate Mr. R. F. Tomes's paper VII. \ on the Fossil Madreporaria of the Great Oolite of Clou- ts cester- and Oxfordshires 195
f Sketch-Map of the St. David's district to illustrate Mr. A. VIII. \ Geikie's paper on the supposed Pre-Cainbrian Rocks of
I St. David's 268
IX. j Rock-sections, to illustrate Mr. A. Geikie's paper on the X. \ supposed Pre- Cambrian Rocks of St. David's 325
YT f Megalosaurus Bucklandi, to illustrate Prof. Owen's paper
\ on the Skull of Megalosaurus 346
yTT f Victorian Ciiilostomatous Bryozoa, to illustrate Mr. A.
\ W. Waters's paper on those fossils 443
XIII. f Basalt-glass, to illustrate Messrs. Judd and Cole's paper
XIV. \ on the Basalt-glass of the Western Isles of Scotland 463
XIV EXPLANATION OF PLATES.
Plate Page
XV.
XVI.
XVII.
XVIII.
XIX. J
^Inferior -Oolite Fossils, to illustrate Eev. Gr. F. Whid- borne's paper 538
XX. f Inferior-Oolite Sponges, to illustrate Prof. Soilas's paper on XXI. [ those fossils 552
vvtT f Corallian and Portlandian Madreporaria, to illustrate
' { Mr. E. F. Tomes' s paper on those fossils 564
XXIII ^ West- Australian Fossils, to illustrate Mr. W. H. Hudle-
' ] ston's notes on a collection from West Australia 595
THE
QUARTERLY JOURNAL
OF
THE GEOLOGICAL SOCIETY OF LONDON.
Vol. XXXIX.
1. The Hornblendic and other Schists of the Lizard District, with some additional Notes on the Serpentine. By T. G. Bonney, M.A., F.R.S., Sec. G.S., Professor of Geology in Uni- versity College, London, and Fellow of St. John's College, Cam- bridge. (Bead November 1, 1882.)
[Plate L]
Contents. I. Preliminary. II. Stratigraphy of the Metamorphic Sedimentary Series and its Relation to other rocks.
III. Microscopic structure of the Metamorphic Series.
A. Micaceous group.
B. Hornblendic group.
C. Granulitic group.
D. Remarks on the structure of these groups.
IV. Age of the Metamorphic Series. V. Further notes on the Serpentine.
I. Preliminary.
In my paper on the serpentine and associated rocks of the Lizard district*, I made a few remarks only on the hornblendic and other schists, as the investigation of that series was foreign to the purpose then in hand, and in the concluding paragraphs I incidentally men- tioned it as being " probably about Lower Devonian age." Soon after the publication of that paper I began to pay special attention
* Quart. Journ. Geol. Soc. vol. xxxiii. p. 884. Q.J.G.S. No. 153. b
2, PROF. T. G. BONNEY ON THE HORNBLENDIC AND OTHER
to the structure of nietamorphic rocks of sedimentary origin, and before long to feel the gravest doubts as to the possibility of the great mass of schists associated with the Lizard serpentines being of the same age as the slaty and little-altered Cornish strata, which belong mainly, if not altogether, to the later Palaeozoic period. Each year's experience with the microscope and in other regions did but strengthen this conviction, which of late I have ventured to express frequently ; but it was not until last Easter vacation that I was enabled to revisit the Lizard. In about ten days of hard work I examined with considerable care the coast sections of " hornblende schists," as indicated on Sir H. De la Beche's map, from the Lizard Head to Porthalla on the east, and to Polurrian Cove on the west. During the major part of this time I had the advantage of being accompanied by my friend and former colleague the Rev. E. Hill, Tutor of St. John's College, Cambridge, whose friendly aid I most gratefully acknowledge. A large series of specimens was collected, and evidence obtained, which to my mind is conclusive as to the vast difference in age between the "hornblende schists " and the slaty group. A number of the specimens have subsequently been ex- amined microscopically, and the results are embodied in the following paper, together with some account of two outlying masses of ser- pentine, which I had previously been obliged to leave un visited.
As on former occasions, Sir H. De la Beche's Geological Memoir of Cornwall and Devon was constantly in my hands, and I cannot forbear again expressing my sense of its thoroughness and value. There are, indeed, some points on which I come to different conclu- sions ; but this is simply because I have had the advantage of using the microscope ; and as regards most of these, I believe that the author had expressed himself more or less doubtfully. Each day's work has but increased my admiration of the genius of the first chief of the British Geological Survey ; and I will venture to say that if he could have had the advantages which we now possess, he would have left little for our generation to do in Cornwall.
II. Stratigraphy of the Metamorphic Sedimentary Series and its Relation to other rocks.
In the paper to which I have referred, 1 state that in addition to the "talco-micaceous" schists of De la Beche and the normal horn- blende schists, there is a third group of greyish granitoid rocks, com- posed mainly of quartz and felspar, sometimes almost a quartzite, sometimes simulating a vein-granite, associated with more- horn- blendic, chloritic, earthy, and (as I should have added) micaceous layers. I may refer to pages 885-7 for a sketch of the general petrology of the series ; but on the present occasion, besides supplying many details, I trust to be able to show that there is, in addition to the "talco-micaceous " and the " hornblende-schist " group already recognized, a third or granulitic group. These, however, form but one series, enumerated in ascending order, the first being charac- terized by rather compact dull-green schists, whose exact mineral composition cannot readily be decided in the field, and by brownish
SCHISTS OP THE LIZAED DISTRICT. 6
mica-schists ; the second by black lustrous hornblende schists, some- times rather massive, sometimes beautifully banded with felspar or epidote ; the third by pinkish-grey quartz-felspar rock closely inter- banded with dark hornblendic or micaceous layers.
I will commence my description with the southern coast of the Lizard, in which the lowest of these groups is well exposed. In places the cliffs forbid a close examination ; but we are able to de- scend to the sea from time to time so as to obtain a good general idea of the group as a whole. It is, however, difficult from the above cause, from the want of conspicuous characteristics in the different beds, and from the frequency of dislocations*, to establish a very exact succession in the minor subdivisions. At the south-west angle of the Lizard Head, called the Quadrant, we find the following series : — a thick mass of corrugated greenish schist, with " cherty " bands, over which is a quartzose rock of rather gneissic aspect (p. 12) overlain by fissile green schist, whose constituents are so minute as to give it a slaty look. These have a general E.S.E. dip of about 25°. At the top of the headland, a little further to the N., is a quartz- ose schist with a slightly steeper dip. I think that these beds are the lowest visible in the series. The coast-line indeed from this point to the serpentine at the south end of Pentreath beach runs nearly N., and S. ; but there is much disturbance, and some discor- dance in the dips. On the whole it is my impression, in accordance with Sir H. De la Beche's views, that we reach higher beds in going northward. At Caerthillian (about a furlong south of the serpentine) the hornblende schist proper is mapped as brought in by a fault. The beds are not in a condition very favourable for examination ; there is undoubtedly a fault beyond which are some hornblendic bands ; but on the whole I am inclined to include all or almost all these beds in the lowest or " tal co-micaceous " group of De la Beche, and think that there is no important dislocation.
Proceeding eastwards from the Quadrant along the cliffs (which face south), we walk over a series of greenish micaceous schists of rather uniform character, until we descend to the sea at Polpeor, and are able to pass for some little distance at the base of the cliffs. The lowest part of these (well shown in a tiny cove on the west of the little beach) consists of a green epidotic schist in thick bands, alter- nating with brownish very micaceous schist, and with occasional lenticular hornblendic bands, sometimes exhibiting imperfect crystals or "eyes " of whitish felspar, which last rock has a resemblance to the typical hornblende schist of the Lizard district. The general dip is to E.N.E., about 40°. These beds continue to the main cove, being often beautifully corrugated on a small scale, and are exposed in the road descending to the beach. The headland bounding the cove on the east consists of a greenish schist with fairly well-marked folia- tion, but very minute constituents, which becomes at times epidotic.
* Faults abound in the Lizard district ; they will be noted in almost every cove, inlet, or sea-chasm (of which they are probably the cause). The generally uniform character of the rock makes it extremely difficult to estimate the amount of vertical displacement ; but, as a rule , I believe it to be slight.
b2
4 PEOF. T. G. BONNET ON THE HOENBLENDIC AND OTHEB
The general dip here is between K".E. and N.N.E. At low tide, a small intrusive mass of a porphyritic diabase * only exposed for a few yards, and rarely more than one yard in thickness, can be seen. It is the only igneous rock which I have detected in this group.
The next cove, bounded on the east by the great headland on which stands the lighthouse, marks the junction of the micaceous with the hornblendic series. This is undoubtedly a faulted one ; but I believe the displacement to be but slight, and after more than one examination I retain the opinion previously formed that there is no real stratigraphical break between the two. The headland consists of hornblende schist, the beds of which dip gently under the lighthouse ; and the same rock is exposed a short distance inland on the road from Lizard Town to Polpeor Cove. From beneath the lighthouse to the Bumble Eock the crags are formed of normal horn- blende schist, with fairly well-marked bedding, which, with minor rolling, dips gently to the E.N.E.
Beyond the Bumble comes Housel Bay, with its fine cliffs. Here the beds of the hornblendic series, which are slightly more massive and epidotic near the little rift at its head, appear to form a very slight synclinal followed by an anticlinal ; but the strike continues W.N.W. to E.S.E., and we seem to rise a little as we proceed in an E.N.E. direction, so that on the whole the beds on the Bumble appear to underlie those of Penolver Point. On the eastern side of this headland the beds are beautifully banded, consisting of dark hornblende and whitish felspar (which weathers a light brown colour), and afford indications of false bedding. The gentle rollings continue to Beast Point, where there is rather distinct lenticular bedding, but on the whole there appears to be a gradual dip to E.N.E. At the Point itself the dip is sharper, perhaps 30°, but there is much contortion. The coast-line now has a general trend to the north, and hence to Hot Point the variable bedding and the disturbances continue. At the base of the latter locality the beds seem to be doubled up, the strike of the roll being N.N.W. Here- abouts the structure of the rock is most interesting. Lenticular bedding is frequent, there are some of the most remarkable instances of false bedding on a small scale that I have ever seen (PL I. fig. 2), and indications here and there of a kind of ripple-drift. It is impos- sible to resist the conclusion that, notwithstanding the great amount of metamorphism, we have here a record of true " current-bedding " (whether by water or by wind) in the original constituents of the rock.
*!Maeroscopically it exhibits a rather compact dark grey ground-mass, in which are scattered numerous elongated crystals of a whitish waxy-looking felspar, up to about "5" in length. Microscopically the ground-mass consists of a fel- spathic mineral full of secondary microliths, with the original structure quite obscured, and of hornblende, often occurring in rather distinct prisms clustered together side by side, besides some grains of iron peroxide. The aspect of the hornblende suggests that it is of secondary origin. The larger crystals of felspar are also much decomposed, and all that can positively be said is that the fel- spar is a plagioclase. I regard the rock as a hornblendic diabase, rather than a true diorite.
SCHISTS OF THE LIZARD DISTRICT. 5
From Hot Point to Perranvose Cove the more uniform dark horn- blende schists continue, becoming sometimes more epidotic, sometimes slightly granitoid as we approach the latter. The dips are variable, being in one place W.NWV., with much faulting and other indica- tions of disturbance ; but on the whole the beds appear to strike to- wards the jS".W. with a dip on the eastern side, so that we probably continue to rise in the series. The beds in the cove itself, dark horn- blende schist with marked epidotic and rare quartzo-felspathic bands, have a rather gentle dip somewhat to the south of E.S.E. Dark hornblende schists with epidotic bands continue, so far as can be seen, to the bay, under the Balk Quarry, where we have the first intrusion of serpentine. On reaching the sandy shore we find here, at the southern end of the bay, a decomposed and shattered schist, probably the normal hornblendic rock, capped, in a little reef beneath the quarry, by a well-marked quartzo-felspathic band, which marks the setting in of the uppermost division of the series.
It may save time to give a brief description of the lithological characters of this group. It is generally rather distinctly stratified, beds of a fairly massive quartzose rock of a purplish-grey colour alternating with darker and more schistose bands. The former varies from a felspathic quartzite, containing occasional flakes of mica or hornblende, to a crystalline quartz-felspar rock, in hand specimens hardly distinguishable from a vein -granite. The darker layers are often rich in mica ; but hornblendic or chloritic minerals are sometimes predominant. Commonly these rocks do not exhibit a very marked foliated structure. Lenticular bedding and even indi- cations of current-bedding are far from rare, and the whole group gives one the idea of having been deposited by rather variable cur- rents in waters of no very great depth.
The results of microscopic examination will be given below. I have felt much difficulty in giving the group a name, but think that on the whole it ma3r best be designated as the " Granulitic group," it being understood that garnets are either wanting, or very small and inconspicuous.
The rocks of this group are well exhibited in the cliffs of the Balk Bay, where, as described in my former paper, they are broken through by serpentine and gabbro, and at low water can be followed for some little distance further north, beyond the " granite-vein," which, as explained in my former paper *, is only one of the grani- toid bands in this group. At a little headland in the bay itself the dip is about 45° N.N.E. The thickness must be considerable, not less than two or three hundred feet and perhaps more ; but the in- terruptions caused by the intrusion of serpentine and gabbro make any estimate most difficult. Beyond this the cliffs are serpentine, and their base cannot be approached ; but after about a quarter of a mile we are able to descend to the shore to Polbarrow Cove, where we find a mass of serpentine intrusive in the granulitic series ; this exhibits close and streaky interbanding of the pinkish-grey and dark varieties. One band of the former, just to the south of a * Quart. Journ. Geol. Soc. vol. xxxiii. p. 894.
6 PROF. T. G. BONNET ON THE HORNBLENDIC AND OTHER
little prominence occupied by a boat-house, has a remarkable grit- like aspect (see microscopic description, p. 18). There is much local disturbance, but the general dip is about 25° N.E. On the north side of the cove serpentine with intrusive gabbro rises to the top of the cliff; these continue for a short distance till a second small cove is reached, bounded on the south by dark serpentine * and intrusive gabbro, both of which break through the granulitic group, and on the north by the normal dark hornblende schist. The cove itself follows the line of faulting, by which the rock for a short distance seems completely ' smashed.'
The latter group was examined from above down to the sea at Carnbarrow. It is the normal dark hornblende schist, with the usual specks and imperfect bands of white felspar, which in one place shows remarkable indications of current-bedding. The beds dip to N.E. or a little N. of this at about 20° to 30°. In the small quarry above Dolor Hugo, where the general dip is about N.E., the highest rock begins to bear some resemblance to the granulitic group. The sedi- mentary beds on either side of the " Prying Pan" belong to the granulitic group, and though locally much disturbed by intrusions of serpentine, appear to have a general dip to the N.N.E. at about 20°.
A great fault passes down Cadgwith Cove and brings in again the dark hornblende schist with epidotic bands and indications of current- bedding (p. 16), similar to what we find above the middle part of this group. The general dip is between N.N.W. and N.W., and about 35°.
These dark hornblendic rocks continue with a fairly steady dip until, after passing another small cove, we come to the (red) serpen- tine quarry on Tnys Head, where that rock is intrusive in a mass of the granulitic group, which also crops out among the serpentine in the headland immediately to the north. The general dip of the stratified series is north-westerly, and at about 30°. A little beyond is a bowl-like corrie with indications of a landslip, which leads us down to the sea. Here we have the black serpentine breaking through and overlying the granulitic group, which is exposed in at least three places, the largest mass, on the southern side of the recess, dipping roughly W.N.W. A thick dyke of coarse gabbro, conspicuously foliated towards the exterior, runs obliquely up the cliff. Some of the diallage crystals are of great size ; one, which appeared fairly unin- terrupted, was more than four inches across.
The sedimentary rocks seen on each side of Caerleon Covef, de- scribed in my last paper, belong to the granulitic group with pseudo- granitic bands as at the Balk. In some cases the layers of granitoid and of dark hornblendic or micaceous rock alternate rapidly, the thickness being from 3" downwards.
The details of the coast rock of Caerleon are given in my former paper, as well as those in Kennack, so that it will suffice to say that the sedimentary rocks belong to the granulitic group, and in the
* The variety found abundantly north of Cadgwith.
t I again examined the dioritedyke (described p. 900). I am now quite sure that there is no hornblende schist entangled in it.
SCHISTS OF THE LIZAED DISTEICT. 7
latter seem to form a kind of littoral fringe to the great mass of ser- pentine inland. Some of the former show