An Essay on the Geology of Cumberland and Westmorland

Front matter

AN ESSAY ON THB GEOLOGY OF CUMBERLAND AND WESTMORLAND. BY HENRY ALLEYNE NICHOLSON, D,Sc„ M.B., F.G.S.. late: baxter scholar in thu natural sciences is the CNIVfcJtSITY OF EDINBURGH. LONDON : ROBERT HARDWICKE, 192, PICCADILLY. MANCHESTER : ALEXANDER IRELAND AND CO., PALL MALL. 186S. iBcincatefc TO HIS FRIEND AND TEACHER, ROBERT HARKNESS, Esq., F.R.S., TROFESSOR OF GEOLOGY IN QUEEN'S COLLEGE, CORK, WITH EVERT SENTIMENT OF RESPECT AND ESTEEM BY THE AUTHOR. PEEFACE. The following essay was originally written as a thesis for graduation as Bachelor of Medicine at Edinburgh in the year 1867 ; and, a University Gold Medal having been awarded to it, I am induced to publish it with such additions and corrections as my subsequent researches have enabled me to make. It cannot lay claim to be considered in any way as an exhaustive memoir, but simply as a brief but careful resume of what was already known upon the subject, amplified where this appeared desirable, and in places modified, by original observations of my own.

In its preparation I have gratefully to acknowledge the great assistance which I have derived from the writings, amongst others, of Professors Sedgwick and Phillips. To Professor Harkness, however, are my thanks especially due, not only for the valuable help, which I have obtained from his published researches, but also for the still more valuable information, which he has imparted to me personally in the many geological excursions which we have made together over the district in question. CONTENTS.

Introduction

. General Structure of the Lake District.— Sub-divisions of the Silurian Rocks— Absence of Lower and Middle Old Red Sandstone— Upper Old Red Sandstone — Carboniferous Rocks — Permian Strata — Glacial Period Page 1 to 10. Eaults of the Lake District.— Two Systems of Faults— Penine Fault— Permian Fault— Other North and South Faults of the District-Older System of Faults — Effects on the Configuration of the two Counties . . Page 10 to 18.

Chapter I

The Skiddaw Slates.— Lithological Characters — Skiddaw Slates of the Keswick Area— Metamorphism of the Skiddaw Slates by the Granite of the Caldew Valley — Skiddaw Slates of Black Comb — of the Ulleswater Area — of the Neighbourhood of Shap — of the Silurian Area beneath the Penine Range — Age of the Skiddaw Slates— Fossils of the Skiddaw Slates . Page 19 to 32.

Chapter II

The Green Slate and Porphyry Series. — Lithology— Distribution in the Lake District Proper — Existence of a Band of Shales containing Caradoc Fossils near their Summit — Green Slates and Porphyries of the Silurian Area beneath the Penine Range — Dufton and Swindale Shales— List of their Fossils — Age of the Green Slates — Igneous Rocks of the Caldbeck Fells . Page 33 to 41. The Granites of the Lake District. —Granite of Wasdale Crag near Shap— Its Mineral Character- Changes Produced at the Junction of the Granite with the Neighbouring Rocks — Glacial Phenomena — General Conclusions - Granite of Eskdale and Wastwater— Granite of Duftnn— Granite of the Caldew Valley— Granite of the Skiddaw Slates of Black Comb . Page 41 to 48.

Chapter III

The Coniston Series. — Sub-divisions — Coniston Limestone — Lithology— Distribution in the Lake Districtin the Furness District— in Ravenstonedale— in Yorkshire — Coniston Limestone of Keisley near Appleby — Age of the Coniston Limestone— Fossils Paj-;e 49 to 55. CONTENTS. Coniston Flags.— Views as to the Age and Position of the Coniston Flags— Sub-divisions of the Group, as seen in Long Sleddale — in Troutbeck — in the Neighbourhood of Ambleside — near Torver— to the South-west of Torver — Fossils of the Coniston Flags — General Conclusions as to the Age of the Coniston Flags Page 55 to 65. Coniston Grits.— Lithology — Distribution — Organic Remains — Age . Page 65 to 68. The Ludlow Rocks. — Distribution — Lithology— Beds with Star-fishes — List of Fossils Page 68 to 71.

Chapter IV

The Upper Old Red Sandstone. — Lithology — Conglomerates near Kirkby Lonsdale— Old Red Sandstone of the Vale of Birbeck — Division into three Groups — Lithology of these — Plant Remains of the Upper Division — Conglomerates of the Ulleswater Area — Upper Old Red of the Penine RaDge — Conglomerates with Scratched Pebbles near Sedbergh . Page 72 to 77. The Carboniferous Rocks. — The Scar Limestone Series— Lithology — Scar Limestone of the Penine Range— Great Whin Sill — Yoredale Series — Millstone Grit- Coal Measures Page 77 to 80.

Chapter V

The Permian Rocks. — Want of Conformity with the Carboniferous Rocks — General Division into Lower, Middle, and Upper Groups —Permians of the Vale of Eden — near Kirkby Stephen — of the Neighbourhood of Appleby — Nature of the Unaltered and of the Magnesian Breccias — Plant Remains of the Middle Permians or Hilton Shales — Permians of the Neighbourhood of Penrith — Relation of the Permians of Cumberland to those of Dumfriesshire —Permian Rocks of the West Coast of Cumberland— of the Furness Area - Haematite— Permian Rocks of Dumfriesshire — Triassic and Liassic Strata Page 81 to 93. GEOLOGY OF CUMBERLAND AND WESTMORLAND.

INTRODUCTION.

. The Geological structure of Cumberland and "Westmorland has been investigated and described by various well-known observers. That the Silurian rocks of the Lake district admitted of division into three great groups was first recognised by Mr. Jonathan Otley, (see " Descriptive Guide to the English Lakes.") These sub-divisions were subsequently elaborated in greater detail, and ably described in several valuable memoirs, by Professor Sedgwick ; whilst their fossils were described and admirably figured by Professor McCoy, in the " Description of British Palæozoic Fossils in the Woodwardian Museum of Cambridge." A general account of the geology of the Lake district has also been given by Professor Phillips, and his " Geology of Yorkshire " may be advantageously consulted, especially with regard to the Carboniferous Rocks of the North of England.

The labours of Professors Sedgwick and Phillips have of late years been supplemented and largely added to by Professor Harkness, who has devoted his attention more especially to the Silurian and Permian groups, and _V B

INTRODUCTION.

. published the results of his investigations in a series of very valuable memoirs, in the " Quarterly Journal of the Geological Society." * In this essay I propose to notice the main facts in the geology of the two counties, which have been established by the combined labours of the above-mentioned observers. Most of these facts I have verified by personal research, and I have been able to add others as the result of original investigation on my part. On looking at a Geological Map of Cumberland and West morland, it will be seen that the Lake district proper is composed of Silurian strata, which are flanked on every side by deposits of a later date, belonging to the Old Red Sandstone, Carboniferous, and Permian formations. The Silurian nucleus has commonly been spoken of as constituting a dome-shaped mass, but there is no single line of elevation, and this expression (as pointed out by Professor Ramsay in the opening address to the Geological Section of the British Association, in 1866) is no longer tenable.

The theory that the older rocks of the Lake district had been raised along an axis of elevation running across the district in an E.N.E. and W.S.W. direction, and that a series of faults diverged from this line, was ably supported by Mr. Hopkins. (Quart. Journal Geol. Soc, voL iv. p. 70.) His arguments, however, are vitiated by the very imperfect knowledge at that time possessed by the majority of geologists as to the structure and correlation of the Silurian rocks, and we now know that no such line of elevation exists. * The chief sources of information concerning the geology of the Lake district are to be found in the writings of the following geologists :— Dr. Buckland, "Geol. Trans.," 2nd series, vol. iv. p. 105, et seq. Professor Sedgwick, "GeoL Trans.," 2nd series, vol. iv. p. 383, et seq.; "Proceedings Geol.

Soc," voLL; "Quart. Journal Geol. Soc." vols. i., ii., iii., iv., and viii. ; "Letters" in Words worth's Guide to the English Lakes ; " Synopsis of the Classification of the British Palæozoic Rocks." Professor Phillips, "Geol. Trans.," 2nd series, voL iii. p. 9: and vol. iv. p. 95.; "Geology of Yorkshire," vol. ii. ; "Black's Guide to the English Lakes." Mr. Hopkins, "Quart. Journal GeoL Soc," vol. iv. p. 70, et seq. Professor Me. Coy, "Description of the British Palæozoic Fossils iD the Woodwardian

INTRODUCTION.

. 3 The main Silurian area comprises, as I have said, the whole of the Lake district proper, having an extent of about forty miles in a N.N.W. and S.S.E. direction, and an average breadth of twenty-five to thirty miles in a W.S.W. and E.N.E. direction. Within this area the general strike of the beds is E.N.E. and W.S.W., and their normal dip is S.S.E., usually at high angles. On tbe north-east margin of the area the Silurian strata are overlaid by the Old Red Sandstone and Carboniferous Rocks, but they reappear, in part, on the same line of strike on the N.E. side of the Permians of the Vale of Eden, forming a remarkable Lower Silurian outlier, which is situated beneath the Penine chain and has been described by Professor Harkness. (Quart. Journal Geol. Soc, vol. xxi.) On their opposite or south-west margin the Silurians again disappear, being overlaid by the Carboniferous and Permian strata of the west coast of Cumberland; but by prolonging the line of strike the lower part of the series, comprising the Skiddaw slates and part of the Green Slates and Porphyries, is again found occupying the greater portion of the Isle of Man, as shown by Professor Harkness and myself.

(Quart. Journal Geol. Soc, vol. xxii.) The Silurian rocks of the Lake district are represented by members of both the lower and upper divisions of the formation, the middle division of the period, if it can be said to have a distinct existence, being apparently wanting. The base of the Lower Silurians is formed by the "Skiddaw slates," a vast series of purely sedimentary beds, attaining a thickness of about 7,000 feet, and representing the base of the Lower Llandeilo or Arenig group. The Skiddaw slates are conformably succeeded by the " Green Slates and Porphyries," a group with a probable Museum of Cambridge." Professor Harkness, "Quart. Journal Geol. Soc," vols. xviii., xix., and xxi. Sir Roderick Murchison and Professor Harkness, "Quart. Journal Geol. Soc," vol. xx. Professor Harkness and Dr. H. A. Niclwlson, "Quart.

Journal Geol. Soc," vol. xxii. ; "British Association Reports for 1867." Mr/ Binney, Mem. Lit. and Phil. Society of Manchester, vols. xii. and xiv. Mr. Wallace, "Mineral Deposits." Mr. Hughes, "G_o_ Magazine," voL iii. p. 206, voL iv. No. 8.

INTRODUCTION.

. thickness of from 7,000 to 10,000 feet, and composed almost entirely of felspathic ashes and interbedded porphyries in regular alternation. The lower portion of the group is not known to contain any organic remains of any kind, and may possibly be of the age of the Upper Llandeilo. The upper portion is mainly composed of ash-beds and porphyries, but contains in the Lake district a fossiliferous band of shales, which expands beneath the Penine chain into a great thickness of black shales, crowded with characteristic Bala fossils. The entire group of the Green Slates may thus be considered with great probability as being partly of Upper Llandeilo and partly of Lower Bala age ; there is, however, no stratigraphical or lithological break throughout the entire group, and the whole may therefore belong really to the Bala period, the total absence of fossils in the lower portion of the series rendering a definite determination at present impossible.

The Green Slates are, in turn, conformably surmounted by the Coniston Limestone with its associated shales, the whole having a thickness of about 300 feet on an average, and being the undoubted equivalent of the Bala Limestone of Wales. The Coniston Limestone is succeeded by a great group of slates, flags, grits, and shales, of which the lower portion was termed the " Coniston Flags " by Professor Sedgwick, whilst he named the upper " Coniston Grits." The thickness of the two groups is estimated by Mr. Hughes, of the Geological Survey, to be between 6,000 and 7,000 feet in the Sedbergh and Howgill districts. This must be fully attained, if not exceeded, in the Lake district proper ; but an accurate estimate can hardly be made with our present knowledge, on account of the numerous undulations and the enormous faults with which the series is affected, as well as from the absence of any continuous section.

That the Coniston Flags and Grits belong to the same group is admitted by all who have studied the subject, but their exact position has been a point of considerable discussion. By Mr. Hughes they are believed to rest uncomformably upon the Coniston Limestone, and to form the base of the Upper Silurians of Westmorland. Professor Harkness and myself have, on the

INTRODUCTION.

. 5 other hand, failed to detect any unconformability or break of any kind, and the Coniston Flags and Grits are believed by us (for reasons which I shall hereafter give at length) to con stitute the top of the Lower Silurian series, having no exact equivalent in the typical Silurian district in Wales. The Llandovery group, in the Lake district, seems to be entirely absent, no strata being known in the two counties, in which the fossils characteristic either of the lower or of the upper division of this formation have been discovered. On the view that the Coniston Flags and Grits are really Lower Silurian, the same observation applies also to the Wenlock group, so that the topmost beds of the Lower Silurians are directly succeeded by the Ludlow Rocks. This must be due either to a want of conformity between the two, or to the influence of an E.N.E. and W.S.W. fault bringing the Ludlow Rocks down against the Coniston Grits.

The base of the Ludlows can nowhere be seen, and it is, therefore, impossible to say which of these is the correct supposition. The latter, however, has most probability, since there is no evidence of any unconformability or overlap, and there are strong grounds for assuming the existence of such a fault in the disposition of the strata at Shepard's Quarry and at Benson Knot, near Kendal, though the exact junction is not exposed. (See Harkness and Nicholson, Quart. Journal Geol. Soc, vol. xxii. p. 484.) The Ludlow Rocks comprise a great series, probably several thousand feet in thickness, of variously-coloured grits and shales, and are charged with characteristic fossils. They are terminated by beds supposed to be analogous to the "tile-stones" of Here fordshire (Sedgwick), and really referable to the higher part of the Ludlows, the summit of the group being nowhere exhibited in consequence of overlapping conglomerates of the age of the Upper Old Red Sandstone.

In all probability both Upper and Lower Ludlow Rocks are present, but no exact line of demarcation has at present been established between them. The noble Silurian series of Cumberland and Westmorland, with the sub-divisions above enumerated, is thus seen to attain an approximate thickness of from 25,000 to 30,000 feet, of which

INTRODUCTION.

. at least 20,000 feet must be assigned to the Lower Silurians. Some of the sub-divisions appear to be very exact equivalents of members of the typical Welsh area ; others are not strictly equivalent to the Welsh groups, but are more properly " homo taxeous," being enormously expanded, and containing special and peculiar families of fossils ; whilst the Coniston Flags and Grits appear to be without any representative in Siluria proper, but to be intercalated as a unique deposit between the Bala Limestone and the Lower Llandovery. Lastly, some familiar groups, as the Llandovery and Wenlock, appear to be entirely absent. There is no satisfactory evidence of the existence of any strata referrable either to the Lower or to the Middle Old Red Sandstone; but the sea-bottom at the close of the Silurian epoch commenced gradually to rise, and at this time were produced certain great E.N.E. and W.S.W. faults, which intersect the Silurian rocks, but leave the younger deposits wholly unaffected.

This gradual elevation continued till near the close of the Devonian epoch, when the land again commenced to sink beneath the sea. The subsidence, however, was not sufficient to submerge the more elevated portions of the Silurian area, which remained as an island in the ancient ocean, round the borders of which and upon the upturned edges of its component rocks, there were then deposited disconnected masses of coarse conglomerate with subordinate bands of sandstone and grit, the whole referable to the age of the Upper Old Red Sandstone. There are reasons for the belief that this Silurian island extended westward towards the Isle of Man, and included the greater part of it. The chief foundation for this statement is in the fact, that the Old Red Sandstone and Lower Carboniferous strata are apparently wanting along the west coast of Cumberland and the east coast of the Isle of Man, whilst the conglomerates of the Upper Old Red reappear again on the west coast of the Isle of Man, reposing unconformably upon the Skiddaw slates in the neighbourhood of Peel.

If this hypothesis be correct the sepa ration of the Isle of Man from the main-land must have taken place towards the close of the Carboniferous epoch, as evinced by the occurrence of Permian strata forming the west coast of

INTRODUCTION.

. 7 Cumberland, and by the fact that the Skid daw slates of the Isle of Man are penetrated by veins of hæmatite, in all probability of Lower Permian age. The annexed is a diagrammatic section across the Lake district and the Isle of Man, which will serve to show the general phenomena which induce me to adopt this view. Fw. 1. w.s.w. Isle of Man. Lake District. E.H.B. Ideal section through the Isle of Man and the Lake district. a. a. Skiddaw slates. — b. b. Upper Old Red Sandstone.— c. Carboniferous rocks.— rf. Permian strata. These same phenomena have, however, been differently construed by Prof. Phillips (see "Black's Guide to the English Lakes," pp. 252, 253), who considers that the western side of the Lake district must have sunk at a rate of subsidence relatively more rapid than that which affected the eastern side, so that the Old Red and Carboniferous Rocks became covered up by Permian deposits, and thus concealed along the west coast.

This, however, could hardly have been the case, unless there existed also a line of fault along the line of junction of the Permian and the older rocks, and of this we have no evidence. The Old Red Sandstone, in fact, seems to be uniformly absent along the west coast of Cumberland, and the Permians appear to rest directly and unconformably upon the Lower Silurian rocks. The Upper Old Red Sandstone of Cum berland and Westmorland presents all the characteristics peculiar to littoral accumula tions, and marks the commencement of a long period of gradual subsidence which continued till the close of the Carboniferous epoch. As already stated, no strata are known which can be referred to the age of the Lower and Middle Old Red Sandstone ; and it is probable that the entire region was

INTRODUCTION.

. gradually rising, whilst the higher portions were sub-aerial, throughout the vast lapse of time represented in other parts of Great Britain by the many thousand feet of sedimentary strata belonging to the above sub-formations. As the sinking of the land continued the coarse mechanical aggregates of the Old Red were succeeded by a series of strata, laid down in quieter seas, but giving evidence of many oscilla tions of level and changes of external conditions. These — the Carboniferous Rocks — as developed in Cumberland and West morland consist in their lower portion of numerous alternations of limestones, shales, grits, and sandstones, with a few small seams of coal and bands of ironstone, attaining a total thickness of nearly 3,000 feet, and capped by the plant-bearing shales and sandstones, with the workable coal seams, of the Coal-measures.

At the conclusion of the Carboniferous period, movements of elevation again took place, by the influence of which the Carboniferous strata were subjected to denudation, and some, probably, of the great north and south faults of the region were produced. These elevatory movements are evidenced by the constant want of conformity between the Permian and Carboni ferous strata, and they were followed by a steady depression of the sea-bottom, which lasted till the close of the Permian epoch, without ever attaining to any great intensity, since most of the Permian strata show signs of having been deposited in seas of no great depth. The waters of the ocean were now charged with peroxide of iron, and the sediments deposited have in consequence a prevailing red colour, and, as is usually the case, exhibit scarcely any traces of organic life.

The amount of iron introduced into the sea at the commencement of the period was so large that a segregation of it took place, giving rise in fissures of the subjacent rocks to tbe enormous accumulations of hæmatite, which are now worked so largely in the west of Cumberland. The Permian rocks are magnificently developed in all their three sub-divisions. The Lower Permians consist of strong siliceous red sandstones, with local breccias sometimes of con siderable thickness. The Middle portion of the series commonly

INTRODUCTION.

. 9 consists of gypsiferous shales and clays, the normal calcareous element being absent or degenerate. The Upper Permians are uniformly composed of sandstones, with intercalated "way boards " of shale in some places. The maximum thickness of the entire group, as seen in the neighbourhood of Penrith, is not less than 8,000 feet, but it is not greater than 3,000 to 4,000 feet in the vicinity of Appleby. It is not improbable that the commencement of the Permian epoch was ushered in by a period of arctic cold, as indicated by the occurrence of certain breccias at the base of the series in the Vale of Eden, which are conjectured with considerable likelihood by Professor Ramsay to be consolidated boulder-clay or glacial drift. Brec cias of essentially the same nature sometimes occur at the top of the Lower Permians, and in one locality between the Middle and Upper groups ; and these probably indicate climatic conditions similar to those which gave rise to the lower breccias.

The Mesozoic rocks can hardly be said to take any part in the formation of the two counties, no traces of their existence being known beyond a small and insignificant patch of Triassic and Liassic strata in the neighbourhood of Carlisle. At some period subsequent to the deposition of the Permian rocks there took place enormous elevatory movements, affecting all the palæozoic rocks alike, which gave rise to some (possibly to all) the great north and south faults of the district, and which very greatly altered the physical configuration of the region. Since the Liassic period Cumberland and Westmorland seem to have remained in the condition of dry land, till the commencement of the Glacial epoch, when a subsidence took place. This, at least, is the most probable view, but all that can be definitely asserted is the absence in the two counties of any deposits referable to the later Secondary or to the Tertiary period.

Even during the Glacial epoch the central and higher portions of the Lake district appear to have escaped submergence, and it seems indeed not unlikely that the Lake mountains were much higher at that time than they now are, though this can hardly be de monstrated. However this may be, it seems certain that the more

INTRODUCTION.

. lofty mountains constituted islands in the Glacial sea, and that the abundant traces of ice-action which they display, must be referred to the agency of land-ice and not to that of icebergs. The chief facts in support of this view are the following : — The boulder-clay in the more mountainous parts of the district derives both its general colour and its included fragments from the rocks in the immediate neighbourhood or proper to the particular hydrographical basin. Further, the same elevated districts show plentiful traces of the action of glaciers in the grooved and striated surfaces of the fundamental rocks, and in the presence of conspicuous " roches moutonnees " and well marked moraines in many places. On the other hand, through out the Cumberland plain and in all the lower parts of the two counties, as well as in Yorkshire, Lancashire, and Cheshire, the boulder-clay contains fragments of rock, which have been de rived from the mountains of the Lake district proper; a fact which can be explained only by invoking the agency of icebergs.

This is seen most unequivocally in tbe well-known instance of the granite of Wasdale Crag near Shap, boulders of which, in enormous numbers and often of very large size, are scattered over a tract of country extending even to the east coast of York shire. Similar, though not equally familiar, is the occurrence of erratic blocks derived from the Lake country in the glacial drift of the plains of Lancashire and Cheshire. These phenomena can be explained only by the hypothesis that these districts were at one time submerged beneath the waters of an icy sea, which washed the shores of the Lake district, and supported an unfail ing supply of rock-laden bergs derived from the enormous glaciers which clothed the Lake mountains. FAULTS OF THE LAKE DISTRICT. In this place it may be as well to give some account of the faults which traverse the two counties, since to this in a very great degree is due the physical configuration of the region.

The subject is one which has attracted the attention of all those who have studied the district, but nothing short of a detailed survey could suffice to elucidate it fully, and I cannot pretend here to

INTRODUCTION.

. give more than a general description of the chief lines of dislocation. As already stated, Mr. Hopkins endeavoured (op. jam. cit.) to prove that the Lake district had been elevated along an axis of elevation crossing the country from E.N.E to W.S.W., and having a series of minor faults directed from it in a radiating manner ; but we now know that this is not really the case. Various faults were described by Professors Sedgwick and Phillips, of which the Penirle and the Craven are the most familiar ; but they laid down no general principle of note. It is to Professor Harkness that we owe the important discovery, that the great faults of Cumberland and Westmorland can all be classed in one or other of two great systems which cut each other at right angles. * The faults belonging to one of these systems have a prevailing E.N.E. and W.S.W. direction, and coincide, therefore, with the strike of the Silurian rocks and with the axes of their numerous flexures.

Like those of the newer system, these faults occur in the North of England wherever the older palæozoic rocks present themselves, but they are incomparably more ancient, since they affect the Silurian strata only, and the irregu larities produced by them were entirely removed by denudation before the deposition of the Upper Old Red Sandstone. The faults of the second and newer system have generally a direction * It was concluded by Mr. Hopkins as the result of his elaborate inquiries into the subject of faults, that a "system" of parallel fissures could not have been formed "consecutively." He did not think that the total elevation must necessarily take place " at once," but he believed that "the whole of any disturbed district characterised by a continuous system of parallel dislocations must have been elevated simultaneously."

If there was any tendency to form a second set of fissures it would be in a direction perpendicular to the system already existing. Although the views of Mr. Hopkins as to the elevation of the Lake district upon a single line of elevation, having an E.N.E. and W.S.W. direction, are certainly without sufficient foundation, there is reason to believe that the above quoted theories as to the production of parallel faults are weD-grounded. The Lake district affords an excellent illustration of this, the entire country being inter sected by two systems of faults running at right angles to each other. The two systems are totally distinct and were produced at different periods, but the different members of each give evidence of being produced during the same geological period, and of being, therefore, in a geological sense, " simultaneous."

INTRODUCTION.

. perpendicular to the former, or from N.N.W. to S.S.E., thus being at right angles to the strike of the Silurian rocks, and corresponding very nearly with theii normal dip. Whilst the date of the older system can be definitely assigned to the interval between the Upper Ludlows, and the deposition of the con glomerates of the Upper Old Red, that of the newer group is not so certain. That all of them were produced after the Carboniferous epoch is certain, that most of them were posterior to the deposition of the Permian strata is equally certain ; and it is not impossible that some were produced even in the close of the Secondary period. Of the N.N.W. and S.S.E. system of faults, the one best known to geologists is the "Penine Fault." This enormous dislocation commences in Dumfriesshire, being seen at Penton Linns on the Liddel, as described by Professor Sedgwick.

(Geol. Trans., 2nd series, vol. iv. p. 385, note.) From this place it is continued in a S.S.E. direction, passing by Lanercost near Brampton, Renwick, Melmerby, Milburn, Dufton, and Hilton, to near Brough, where it gradually diminishes. On its eastern side the Old Red Sandstone and Carboniferous rocks, and, when the throw has been sufficiently great, the subjacent Silurians also, have been elevated to form the noble escarpment of the Penine range, which presents us with the rare phenomenon of the up-throw side of a great fault not entirely removed by subsequent denudation. On the western side of the fault the Upper Permians are seen to be brought abruptly down against the basement beds of the escarpment, which are now Silurian, now Old Red Sandstone, and now Carboniferous. (See figs. 2 & 3.)