The Scenery of England and Wales, its character and origin, etc

Front matter

THE SCENERY OF ENGLAND AND WALES. LONDON: PR-NTED ET SPOTTISWOODE AND CO., NEW-STREET SQUARE AND PAELIA1IENT STBEET Fig. 31. View of the N.E. Cliffs nf the Peak of Snowdon, forming the S.W. wall of Gins Llyn Cwnithe steepness not exaggerated, THE SCENERY OF ENGLAND AND WALES, ITS CHARACTER AND ORIGIN : BEIXG AN ATTEMPT TO TRACE THE NATURE OF THE GEOLOGICAL CAUSES, ESPECIALLY DENUDATION, BY WHICH THE PHYSICAL FEATURES OF THE COUNTRY HATE BEEN PRODUCED. FOUNDED ON THE RESULTS OF MANY YEARS* PERSONAL OBSERVATIONS, AND ILLUSTRATED BY EIGHTY-SIX WOODCUTS, INCLUDING SECTIONS, AND VIEWS OF SCENERY FROM ORIGINAL SKETCHES OR FROM PHOTOGRAPHS. BY D. MACKINTOSH, F.G.S., Author of Papers on Denudation in the ' Quarterly Journal of the Geological Society,' ' Geological Magazine,' ' Intellectual Observer,' &c. LONDON : LONGMANS, GREEN, AND CO. 1869.

TO SIE EODEEICK IMPEY MUECHISON, BAET. K.C.B., G.C. ST.A. & ST.S., D.C.L., LL.D., M.A., F.R.S., F.G.S., F.L.S. Hon. M.R.S. Ed., & R.I.Ac, MEMBER OF THE INSTITUTE OF FRANCE, DIRECTOR-GENERAL OF THE GEOLOGICAL SURVEY OF THE BRITISH ISLES, &c. Sir Roderick, — With your permission I dedicate this work to you, for the following reasons : — The extent to which the discoveries long ago announced in the concluding part of your Silurian System illustrated the surface-geology of the western part of South Britain, and explained the marine denudation of many physical features, and the marine deposition of extensive beds of drift at the period when an arm of the sea, including the ' Straits of Malvern,' converted Wales into an island. Your having given a name and a system to a series of sedimentary strata, and interbedded igneous rocks, which form the most striking scenery of the country described in this work.

Tour having all along (as is evident from your writings) been guided in your researches by an appeal to Nature, irre - spectively of prevailing theories. DEDICATION. Your having persisted, during many changes of opinion, in advocating efficiency as the main requisite of a geological cause. My belief that all theories relative to the denudation of this country must be chiefly tested by reference to the Silurian districts of Wales, the Welsh borders, and the NW. of England. The attention you have paid to some of my papers on Denudation read before the British Association and Geological Society, or sent to you for inspection. For these and other reasons I can think of no one to whom I can so appropriately dedicate this work as to yourself, notwithstanding that your views may not coincide with some of the opinions therein advocated. D. MACKINTOSH.

Preface

. The object of this work is in some measure to supply a want which the author believes is still felt by the general geologist, physical geographer, intelligent tourist, and heads of educational establishments, namely a detailed and systematised description of the more definite forms assumed by the natural scenery of Eng land and Wales, and a full consideration of the causes to which they owe their existence, so far as they are the effects of denudation. The author would not have ventured upon such a task were it not that his occupa tion as lecturer on geology, &c, to provincial scientific institutions and schools, has furnished him with opportunities of visiting and revisiting almost every part of England, and a great part of Wales. Until lately, he purposely refrained from reading very much on the subject of denudation, lest a bias should be given to his opinions.

On consulting the principal works and papers,* which treat of the denudation of England and * Among the works which treat more or less of this subject may be men tioned the following : — Conybeare and W. Phillip's Geology of England and Wales (denudation of the SW. of England) ; Lyell's Principles and Elements (sea-coast erosion, and denudation of the Weald) ; Murchison's Silurian System and Siluria, 4th edit, (denudation of Wales and the Welsh borders) ; Ramsay's Geological Survey Memoir on the Denudation of South Wales, and his Physical Geology and Geography of Great Britain. The subaerial

PREFACE.

. X Wales, he has found that their contents are either general, or limited to particular localities, so that his difficulty has not been to steer clear of what has already been written, but to arrange and generalise the com plicated results of his own imperfect observations. I am conscious that many localities worthy of being described have been either omitted or slightly noticed, because it would require several volumes to include a full account of them all. I am likewise conscious that a second and more careful survey of the localities I have visited, and even revisited, would be necessary to the production of a work in all respects satisfactory. But my object will be gained if I have said enough to stimulate the geologist and intelligent tourist to farther observation. The work has been divided into three books — the first, or introductory book, being on the causes of denudation and origin of natural scenery in various parts of the world, as a preparation for better understanding the true form of the ground, and the conditions under which it may have originated in our own country.

The western coast of Ireland, which now probably re presents (at least partly) the former sea-shore con ditions of the western parts of England and Wales, has been somewhat particularly noticed. The second and main portion of the work has been devoted to a classification, description, and attempted explanation of the various forms or types of scenery in England and theory has received its most extreme development in Colonel Greenwood's Bain and Rivers, and Mr. Archibald Geikie's Scenery of Scotland viewed in its connection with its Physical Geology. In the Quart. Journ. Geol. Soc, Professor Jukes has applied the subaerial theory to the denudation of the south of Ireland.

PREFACE.

. XI Wales, the principal of which I have been led to include under the heads Escarpments, Cwms (English Comb, Combe, Coomb, Irish Coom, Scotch corry, Welsh Cwm), Passes, Longitudinal Valleys, and Transverse Gorges. In the third book (Excursions) the different classes of phenomena occurring in particular districts have been viewed in connection, and the subjects treated in a more popular style, for the sake of the general reader. Since the appearance of my article on the Brimham Rocks, in the ' Geological Magazine' for April 1865, a great number of articles have been written in the same periodical by myself, Professor Jukes, Mr. G. Maw, Mr. Topley, Mr. Wynne, Mr. Kinahan, Mr. Hull, Mr. Green, Mr. Whitaker, Colonel Greenwood, the Eev. O. Fisher, and others. The reader of the ' Geological Magazine ' will see that, in some parts of this work, I have quoted myself, though not to an extent exceeding ten or twelve pages.

I still advocate the views suggested to my mind while in the field, and it will be found that so far as denudation is concerned, they more or less agree with opinions held by Sir R. I. Murchison, Sir Charles Lyell, Professor Phillips, Mr. C. Darwin, and others.* I have, however, endeavoured to represent fully, and up to the moment of writing, the state of opinion among the advocates of subaerial denudation, that the reader may be able to judge for himself. I have had great difficulty in obtaining appropriate illustrations. Of many phenomena I took sketches on * It may be remarked that those surveyors who are the most extensively and practically acquainted with the varied forms and kinds of escarpments, drifts, soils, and sea-coast phenomena, namely, Mr. Hull, Mr. V. Searles Wood, jun., and Mr. Kinahan, are advocates of marine denudation.

PREFACE.

. the spot, which are faithful as regards outline, steepness of slope, &c, though imperfect as artistic efforts. In the case of other phenomena I have been at some pains to secure photographs in neighbouring towns, the un satisfactory nature of which, in common with all photographs (the background being generally taken out of focus), I have to a certain extent remedied by super imposing distinct outlines. I have seen few published engravings of much value as regards accuracy of outline, the steepness of the slopes being generally exaggerated, and the planes (of great importance in connection with denudation) represented by more artistic (?) wavy or zigzag lines. All the views of scenery have been taken from original sketches, or from photographs. They have all been engraved purposely for this work.

In conclusion I may state that I have written this work under the belief that nothing can be more detri mental to the progress of a science than an attempt to enlist sympathy in favour of a theory on the ground of its being new, or to excite a prejudice against a theory because it is old; that in true science old aud new fashions avail nothing ; and that an appeal to Nature, irrespectively of schools or parties, ought alone to be the guide of inquiry. If I have been influenced by any principle or rule of investigation, it has been — that in endeavouring to explain a phenomenon, we ought never to overlook the main requisite of a cause, namely efficiency, or to forget that though time may develope efficiency it cannot confer it. PAGE CONTENTS.

Book I. Introductory Remarks On Tne Causes Of De- Nudation, And Origin

OF NATURAL SCENERY IN VARIOUS PARTS OF THE WORLD. Connection between Denudation, Upheaval, and Lines of Fault and Fracture — Theories of Denudation — Its Commencement on Unequal Surfaces of Deposition — Irish Eskers — Submarine Inequalities — Denuding Action of Oceanic Currents and Waves in Various Parts of the World — Sea-escarpments of Croaghaun and Slieve League — Sea-coast Cwms — Forbes and Darwin on the Denudation of Norway, South America and Australia . 3

Part I. Denuding Action Of The Sea On The Coasts Of England

AND WALES. CHAP. I. Denuding Action of Tidal Currents. — Currents of the Menai Strait and Bristol Channel — What is Denudation ? — Effects ofa very High Tide in Morecambe Bay .25 CONTENTS. XIV PAOE CHAP. II. Denuding Action of Sea-waves.— Power of Sea-waves — Their Action not confined to Cliffs— Effects of the Ground-swell— Mode of Encroachments of the Sea in the Bristol Channel, at Bosham, on the south coast of the Isle of Wight- Supra-marine Sea-cliffs— Alternate Encroachment and Deposition . 31

Part II. Classification And Origin Of The Sea-coast Scenery Of England And

WALES. I. Inequalities and forms of Rock-surfaces under Water. — Inequalities adjacent to Coasts — Submarine ' Screes' — Rounded. Hollowed, Grooved, Honeycombed, and Bored Rock-surfaces under Water .......... 42 II. Forms of Sea-beaches. — Shingle and Boulder Beaches — Interweaving of Pebbles with Sand, &c. — Terraces at different Tidal Levels — Imbedding of Angular Fragments — Block-beaches . 45 III. Varieties of Sea-cliff Architecture. — Cliffless Sea-shores — Irregular and Regular Cliff-lines — Undercuts, Caves, Horizontal Grooves and Ridges in Cliffs — Basin-shaped Cavities — Perforations and Arches — Needles, Stacks, &c. — How far the Atmosphere denudes Sea-cliffs ........ 50 IV. Forms of Sea-coast Inlets. — Straight and Winding Lines of Cliff — Bays, Coves, Coast-slip Coves, Narrow Inlets, Voes, and Creeks — Power of the Sea in Inlets . . . . . .58

Part III. Denudation During The Glacial And Other Sub- Mergences Of England

AND WALES. I. Preglacial Submergences 66 H. Denudation during the Great Glaciax Submergence. — Alleged Dormancy of the Glacial Sea — Why Ice-marks were not effaced — Marine Drifts regarded as a measure of Denudation — Marine Drifts of Shropshire, Herefordshire, Wales, and North- West Lancashire — Connection between Deposition and Denudation — Missing Drift Deposits — Marine Angular Drift — Theory of the Non-submergence of the South of England controverted — Duration of the Glacial Submergence, &c. . . CONTENTS. XV CHAP, I. II. III IV. V. VI.

Part IV. Classification And Origin Of The Inland Scenery Of England And Wales

PAGB Correspondence between Scenery and the Structure of Rocks 80 Raised Sea-beaches and Inland Terraces. — Weston-super- Mare Raised Beach — Terraces of the Liassic, Oolitic, and Cretaceous Districts — Terraces near Stockbridge and Twyford — Origin of the Terraces of the Chalk Downs — Terraces near Llangollen — Relative Amount of Gradual and Sudden Upheaval . .83 Inland Escarpments, Cwms, Cliffs, and Rocky Projections — The Cretaceous, Oolitic, Triassic, and Carboniferous Districts. — General Remarks — Theory of Fracture — Escarpments of the Weald — Their Marine Origin advocated in opposition to the Subaerial Theory of Greenwood, Jukes, Foster, and Topley — Chalk Escarpments not Denuded conformably to Structure — Escarpments of Hants, Wilts, and East Devon — Black Downs and Haldons — Oolitic Escarpments — The Great Cotswold Escarpment — Bredon Hill — Liassic Escarpments of Somersetshire — New Red Sandstone, Permian, Coal Measures, and Millstone-grit Escarpments — ' Sea-shore Rocks ' of the Peak — Wharncliffe and Plumpton Rocks . . . .95 Inland Escarpments, &c. continued. — The Brimham Rocks. — Traces of Marine Denudation — Anvil, Mushroom, Table, and Tree-shaped Rocks — Rock-basins and Rocking-stones — Perforated Rocks — Reflections 119 Inland Escarpments, &c. continued. — Mountain Limestone Escarpments, Cliffs, Caves, &c. — Westmoreland and Derbyshire — The Orme's Heads and Eglwyseg Cliffs — Somersetshire — The Cheddar Cliffs— Their Origin— Claims of different Theories considered — Old Red Sandstone Escarpments — The Black Mountain, Brecon Beacons, &c. 124 Inland Escarpments, &c. continued. — Escarpments, Cwms, and Cliffs of the Silurian Rocks of Wales and the Welsh Borders. — South Shropshire, Llangollen, Corwen, &c. — Cliffs near Rhayadr — Escarpments, Cwms, and Cliffs of Cader Idris— Cwm-y-Gader, and Cwm Cae — Section of Cader Idris — Escarpments, Cliffs, and Cwms of Snowdon — Section of the Mountain — Denudation — Sea-coast Action — Recent Atmospheric Action — The Cwms of Snowdon not explicable by Rain or Landslips—Contemplations—General character of Snowdonia .

CONTENTS. XVI PAGE CHAP. VII. Inland Escarpments, &c. continued. — Escarpments, Cwms, and Cliffs of the Lake District. — Escarpments facing the East and Various Directions — Helvellyn, "Wanthwaite Crag, Saddleback, &c. — The Pillar Rock — Wastwater Screes, &c. — Blea Water Cwm— Origin of Screes and Rakes — Origin of Scarped Peaks 163 VIII. Inland Escarpments, &c. continued. — Cambrian Escarpments and Cwms — The Malvern Hills . . • .176 IX. Origin of the Granitic Tors, Rock-basins, &c. of Dartmoor and Cornwall. — Bodily Removal of Blocks — Bowerman's Nose and Cheesewring — Rock-pillars — Hey Tors — 'Boss and Tail,' near Morton-Hampstead — Distinction between Rain-worn and Wave-worn Rock-basins . . . • .178 X. Facts and Considerations bearing on the Origin of Cwms and Small Lake-basins. — Typical Forms, Transverse Sections and Boundaries or Walls of Cwms — Form of the Ground under Cwms — Positions generally occupied, and Points of the Compass faced by Cwms — Small Lake-basins — Detrital Accumulations in front of Lakes — Theories of the origin of Lake-basins: Nestling Glaciers, Great Flow of Land Ice, Grounded Icebergs, Deflected and Eddying Currents, and 'Waves of Translation' — Origin of Cwms irrespectively of Lake-basins — Rain, Retrogressive Streams, Springs, and Sea-coast Action — Concluding Facts and Considerations — Origin of Edges ......... 187 XI.

Remarks on Detached and Conical Hills .... 205 XII. Origin of Table-lands and Plains. — Denudation of Table-lands — Black Down Table-lands, &c. — Table-lands of the Mendips — Salisbury Plain — The Black Mountain — Table-lands of the Peak and Lake District — Intermediate Plains — Origin of Lowland Plains — Marine Origin of Plains proved by their coincidence with the Convexity of the Globe — Principal Plains of England and Wales .... 207 XIII. Classification and Origin of Valleys. — Valleys formed by Sea-coast Action and Currents — Longitudinal Valleys, A7alley-expansions, Basins, and Plains connected by Transverse Gorges — Devonshire, the Chalk Districts, Somersetshire, Clifton, Clevedon, South Herefordshire, Monmouthshire, Breconshire, North Herefordshire, South Shropshire, Llangollen, Central Wales, Rhayadr, the Lake District, Borrowdale, and Watendlath — Theories Relative to the Origin of Longitudinal Valleys and Transverse Gorges — Greenwood, Jukes, Whitaker, Foster, Topley — Objections to the Subaerial Theory — Opinions of Herschel, Ramsay, Murchison, Lyell, and Darwin— Denudation of Valleys encircling Central Domes CONTENTS.

XVII CHAP. XIV. PAGE Origin of Valleys continued — Passes and V-shaped Sloping Valleys. — Passes of Devon, Somerset, Longbottom, South Wales, North Wales, Tal-y-llyn, Bwlch-drws-ar-dudwy, Llanberis, Llyn Ogwen, the Moel Fammau range of Hills, Shropshire, the Lake District, Gatesgarth, Whinlatter, Grisedale, Kirkstone, Dunmail Raise, Mickledoor, &c— Origin of Passes — Claims of Freshwater Streams and Oceanic Currents considered — V-shaped Sloping Valleys — their Connection with Passes — Zone of maximum Fluviatde Denudation— Gulleys of the Malvern Hills 248 XV. Denuding Action of Freshwater Streams, Rain, and Ice. — Delineation of Streams on Shaded Maps — Facts showing the limited Extent of Fluviatile Denudation — Relation between River-channels and the adjacent Form of Ground — Dry and Wet Depressions — River-channels in Drift — Turbidity and Transparency of Rivers — Denuding Power of Rivers not to be measured by the Quantity of Matter they bring to the Sea — Mode and Extent of Fluviatile Deposition — Retrogressive Excavation by Waterfalls — River-channels of S. Britain compared with those, of other Countries — Theory of Former Increased Fluviatile Action — Action of Rain-torrents — Y-shaped Rain-gutters — Action of Rain on Heaps of Coal Mine Rubbish — Diffused Action of Rain — Chemical Action of Rain — Perpetuation of Smoothed, Rounded, Hollowed, and Grooved Surfaces of Limestone Rock, and Lithodomous Perforations — Denudation of Street-pavements — Denuding Action of Ice — Mutually Preserving and Destroying Power of Ice and Water — Glacial and Marine Denudation Compared — Inequalities of the Earth's Surface mainly of Marine Origin 270

Book III. Excursions, With Geological And Miscel- Laneous Observations And Reflections

I. From Miner a to Llangollen, by way of the World's End — An Episode in the Geological History of Llangollen Vale 297 II. From Conway to Llyn Dulyn ...... 305 III. From Bethesda to Carnedd Llewelyn, and back through Cwm Llafar 307 a CONTENTS. XVIII PAGE EXCURSIONS, continued— IV. From Bethesda to Nant Francon, Llyn Bochlwyd, and Llyn Idwal 31" V. From Bangor to Snowdon by the Llanberis Route. — Old Sea-strait — Mynydd Mawr — A Group of Cwms — Fate of the Rev. Mr. Starr— Cliff above Llyn du'r Arddu— First Sight of tho Peaked Promontory of Snowdon — Fate of a Botanical Guide — Precipices of Snowdon — Cwm Glas — Reflections — Disfiguring Action of Rain 315 VI. From Llanberis to Snowdon through the Pass, and by Llyn Llydaw. — Lee-side Smoothing of Rocks — Low-level Cwms — Screes in Llanberis Pass — Perilous position of a G-oat — Culminating Level — Successive Plateaux and Lake-basins — Lliwedd Cliffs — Rock-basins of Llyn Llydaw and Glasllyn lined with Drift — Rutting Action of Streams . 322 VII.

From Dolgelly to the Peak of Cader Idris. — Region of Prostrated Columns — Peaked Isthmus — Dangerous Precipices ......... 330 VIII. From Rhayadr to Cefn Coch, Nant Gwyllt. — Gorge, River and Fallen Blocks — Solitary School-house — Scenery of the Elan . . .334 IX. Around Builth — Abereddw Cliffs 337 X. From Exeter to Budleigh .Salterton — Autobiography of a Pebble. — Marine Origin of the Valley Gravels of Devonshire ......... 342 XI. From Ashby-de-la-Zouch to Charnwood Forest . . 349 XII. A Walk over Malvern Wtch — A Midnight Waking Dream of the Lapse of Time 352 XIII. Around Bewdley. — Declining Days of the Severn Sea — Devil's Spittleful — Habberley Valley . ■ . . 355 XIV. From Wolverhampton to an Icefloe-cargo of Boulders. — Triassic Escarpment — Trescott Boulders — Form of Striations — Reflections ... .... 357 XV.

Around Ironbridge and to the Summit of the Wrekin. —Valley Expansion and Outlet Gorge— Landslips— Felspathic Crags— The Wrong Thing in the Wrong Place- Upland Pass 2Q> XVI. Around Church Stretton and up the Longmynd Gulleys —Reflections on a Worm-burrow— Church Stretton Pass — Ashes Gulley— Abrupt Commencement of Stream-channel — Three-fold Origin of the Longmynd Gulleys .Arenicolites Didyma „g_ XVII. From Shrewsbury to the Stiper Stones. — Signs of a . Sweeping Donudation — Levelling of Transported Detritus . CONTENTS. XIX excursions, continued — page XVIII. From Wem to the Hawkstone and Grinshill Cliffs. — Old Ocean-bed — Red Castle and Grotto Hills — Main Line of Cliffs — Cwms of Hawkstone Park — Grinshill . . 375 XIX. Around Keswick — Model-looking Scenery — Wallow Crags — Waterfalls — Parody on Southey's ' Lowdore ' . .380 XX.

From Coniston to Tilberthwaite, Goat's Water, the Old Man, ANb Greenburn — Twilight Contemplations. — What is a Glacial Moraine? — Blind Tarn, Goat's Water, Dow Crag — Successive Plateaux — Glaciated Rock-surfaces — Distinction between Drift, Moraines, and Screes — Sand and Gravel — Boulder-clay and Loam — Lever's Water — Greenburn Valley ........ 384

Appendix

. A. Cliffs, Beaches, and Lithodomous Perforations near Buxton . 397 B. Excavation of Caves 398 a2 LIST OF ILLUSTEATIONS. o. from Original Sketch, p. from Photograph, q.j.g.s. from the Quarterly Journal of the Geological Society, g.s. from the Publications of the Geological Survey. FIG. PAGE 1, 2, 3, 4. Forms of Valleys, o 19 5. Sea-coast near Watchet, o. . . . . . . . .35 6. ShiDgle-terraces near Budleigh SaltertoD, o. .... 48 7. Sea-worn Chink, Cornwall, p. ....... 55 8. Sea-coast Pillar near Watchet, p. ...... 56 9. Brent Knoll, o 84 10. Terraces near Stockbridge, o 87 11. „ „ Twyford, o 88 12. ,, „ Llangollen, o 93 13. Kingley Bottom Cwm, o 99 14. Escarpment and Plain near Maidstone, q.j.g.s 102 15. Black Down Escarpments, o. ...... . 106 16. Liassic Escarpment, o. . . . . . . . .113 17.

Idol Rock, Brimham, p 122 18. High Tor, Matlock, p 127 19. Groove, Great Orme's Head, p 129 20. „ Little Orme's Head, o 129 21. Eglwyseg Cliffs, Llangollen, o 131 22. Section of Limestone Escarpment, Somersetshire, o. . . .134 23. View of ditto . . . 135 24. Section of Cathedral Rocks, Cheddar, o 136 25. Cheddar Cliffs, p 141 26. Section of Black Mountain Escarpment. Siluria . . . .142 27. Brecon Beacons, o. . . 1*4 28. Cwm near Ehayadr, o. 1*7 29. Cwm-y-Gader, Cader Idris, o 149 30. Section of Cader Idris, G.s LIST OF ILLUSTRATIONS. XXII FIG. PAGE 31. North-east Cliffs of Snowdon, p. and o., Frontispiece 32. Map of Snowdon, Ordnances. ....... 153 33. Section of Snowdon, g.s 154 34. Section of Rain-rut, o 160 35. Section of Cliffed Ridge, o. . . 160 36. Rakes on Wanthwaite Crag, o 166 37. Pillar Rock (s. Mr. Whitehead, Whitehaven) . . . .169 38.

Scawfell, from Old Man, o 170 39. Dow Crag, near Coniston, o. . . . . . . .171 40. Rakes on Great End, o 173 41. Cwms near Malvern, o. ........ 177 42. Part of Rippon Tors, Dartmoor, p 179 43. Bowerman's Nose, Dartmoor, p. ...... 180 44. Cheesewring, Cornwall, p. . . . . . . . .180 45. Outline of Hey Tors, Dartmoor, o. . . . . . .182 46. Blackenstone 'Boss and Tail,' o. . . . . . . .183 47. Rain-worn Basin, o. . . . ...... 186 48. Wave-worn Basin, o. . . . . . . . . .186 49, 50, 51. Typical Forms of Cwms, o. ..... 187 52. Transverse Section of Cwm Bochlwyd, o 195 53. Ditto of Cwm Dulyn, o 195 54. Breidden Hills, o 206 55. View of Tryfan Mountain, o. ....... 206 56. Outline of Black Down Table-lands, o. . . ' . . . 210 57. Section of High Peak Table-land, q.j.g.s 214 58. Gorge near Rhayadr, o. ....... 235 59.

Gorge and Basin near ditto o. ...... 235 60. Gorge and Valley-Expansion of Borrowdale, p. . . . 238 61. Section of Longitudinal Valley and Gorge, o. . . . 239 62. Section of Woolhope Valley (Sduria) .... 247 63. Longitudinal Section of a Pass, o. . . 250 64. Tal-y-llyn Pass, p. .... 253 65. Map of Ogwen Pass (Ordnance s.) . . 955 66. Passes in Denbighshire, o. . . . . osf 67. Dunmail Raise, p. nor, 68, 69. Plan and Section of Valleys connected with Passes, o. 264 70. Gulley near North Malvern, o. 0fi() 71. Sections of Dry and Wet Valleys (Sir H. De la Beche) ' 079 72. Pistyll Rhaiadr Waterfall, p. ' '- 73. Llyn Dulyn, 0 ' "^ 74. Cwm Llafar and Carnedd Dafydd, o. . 75. Nant Francon and Cwm Bochlwyd, o. . 76. Snowdon from the NW., 0. . 77. Goat on Brink of Cliff, o. 78. Dark and lofty Cliffs of Lliwedd, o. . • 3^7 79.

Effects of Wave-action and Weathering, 0. a' ■ ■ ■ . LIST OF ILLUSTRATIONS. XXlil FIG. PAGE 80. Section of Drift near Newbridge Station, o 340 81. Stream-channel, Longmynd, o. ...... . 368 82. View of the Stiper Stones, o 373 83. Sections of the Stiper Stones Ridge, o. 373 84. Wallow and Falcon Crags, p 382 85. Low Water Cwm, Coniston, o 390 86. Section of Associated Boulder-clay and Loam, o Errata. Page 91, line 14 from top, for slightly read nearly. „ 116j line 11 from top, for Shuntingslow read Shutlingslow. „ 117, line 4 from bottom, for WharnclifE read WTiamcliffe. „ 181, line 19 from top, for Redruth read Liskeard.

Book I. Introductory Remarks On The Causes Of Denudation, And Origin Of

NATURAL SCENERY IN VARIOUS PARTS OF THE WORLD. E

BOOK I INTRODUCTORY REMARKS ON THE CAUSES OF DENUDA- TION, AND ORIGIN

OF NATURAL SCENERY IN VARIOUS PARTS OF THE WORLD. All geologists are more or less agreed that, at a distance from recent theatres of volcanic action, the smaller in equalities of the earth's surface are, in most cases, due to the excavating power of water and ice — -in other words, that the present, generally speaking, is not the surface produced by upheaval or depression, but by denudation. Many considerations render it certain that the last upheavals * of the north of Europe, at the close of the glacial and post-glacial submergences, must have converted many horizontal into inclined planes, and left a greater or less number of shallow depressions, while previous upheavals may have given rise to more marked inequalities ; but it is still true that the more abrupt and more abruptly-bounded inequalities are mainly the effect of denudation, f The valleys of the south-coast * The juxtaposition of slowly-subsiding and rising portions of sea-coast, since the glacial period, must likewise have slightly altered the contour of the surface. f Since the above was written, the Duke of Argyll ( Quart.

Journ. Geol. Soc. vol. xxiv., No. 95) has endeavoured to show that the physical features of Argyllshire are mainly the effect of subterranean forces. So far as South Britain is concerned, the relative amount of superficial inequality resulting from upheaval or depression, and denudation, resolves itself into the following questions : — How far does the inclination of surface correspond with the inclination of the underlying strata ? How far have these strata, since they first formed the surface, been covered up by newer deposits, which have been b SCENERY OF ENGLAND AXD WALES. 4 of East Devon, long ago described by W. Phillips Omy beare, and Buckland, afford very obvious illustrali' jus nf the formation at tfidleja by excavation. On sailing ajopjf the shore, tLc toast ignorant person must at <'ii. ■• p.-iv-'ive Hint the approximately horizontal strata, once .•xteuded continuously across, for they precisely corre sipMinl on both aides of the valleys.

Dv.ni(>li>ii<>n nhwq Iritiffl of FfinU arid Ftnrtiin. — It is undeniable that many valleys run along lines dl fan!'. and may therefore have had tlieir rlirwtiou determined, and tlit? ' initiation ' of tlieir excavation faoilitatud by the effect of upheaval or depression. Witli regard to fractures, which have not, disturbed the strata to any great distance around, I thint tlieir importance, in a • l-jimdatioual puint of vi.-w. has been much underrated. Snrh n winding and bifurcating rent as that which occurs behind the main mass of the EEigh T^r, at Mat l"ok, and such rents as are common in the carboniferous limestone of all countries, would be very likely to become enlarged into ravines, if subjected to the long omtiuued action nf running water, or sea-waves (sat Traimiirse Qofgit) ; and the sides of the ravines thQS ?w<pt sway ?

In tlm Menilip antk-lioiil, i'or fnstOnc*, dftanilntifm haa fj.ared Ulaek D.-.vtn. hh'1 utlj^r «'nlnil while 11 las MMJpi .1 thr Vale of W-iLscombc out -i" I,Um «.ry bciiri uT'lic SphedyaJ nui>s of iiraui. THEORIES OF DENUDATION. 5 formed might exhibit little or no disturbance in the corresponding position of the strata. Even in compara tively solid hills, like the Malverns, there are many fissures filled with trap breccia, &c* These represent areas of deposition by currents, waves, and possibly by freshwater. Many other fissures, however, may have existed in areas of denudation, and may have been enlarged into valleys. The fact of numerous fractures having become filled up, is no more a proof that other fractures may not have been denuded, and more or less obliterated, than the fact of deposition in one part of a sea-coast, is a proof that another part is not under the influence of denudation.

Fractures lying in the direction and course of rapid currents, or exposed on parts of sea-coast undergoing destruction, must have been enlarged ; and in the case of fractures previously filled up, the intruded matter may either have been scooped out (as trap dykes are now in course of being scooped out on the west coast of Ireland, &c), or may have remained while softer rocks on one or both sides were washed away — in either case giving a direction to the denudation.f Brief Notice of Tlieories of Denudation. — Hutton and his illustrator, Playfair, were perhaps the first to attempt a philosophical explanation of the excavation of valleys. Playfair believed that there is no part of the land where rivers have not once flowed — that a longitudinal valley consists of two valleys, with their common outlet in a transverse gorge cutting through a ridge — that marine currents cannot form valleys gradually increasing in size from the watershed downwards — that the tidal * See Dr. Holl's paper on the Malvern Hills, Quart.