madeinatlantis LONDON TRAVEL GUIDE THE ENGLISH PLAIN IN few equal areas on the globe is there a more varied accumulation of the newer rocks than in the English plain. Between London and Chester a traveller would cross in regular succession deposits of all ages, from the early Tertiary down to the beginning of the New Red. The centre of the plain, round Birmingham, consists of New Red Sandstones and Clays, and these deposits spread from this point in three directions: along the lower Severn towards Bristol; through the Cheshire Gap to Liverpool; and along the lower Trent and Yorkshire Ouse to the mouth of the Tees. Westward and northward the New Red formation laps round the Cambrian and Pennine uplands, where their rocks sink into the ancient floor underlying the clays and sands of the plain; but eastward and south-eastward it is overlaid by an edge or escarpment of Jurassic limestone, and borings have proved that it extends for some distance in these directions under the covering of later deposits. The Jurassic escarpment curves across England from Cleveland in the north to the Cotswolds in the south-west, and the limestone beds, which are cut short along its front, dip gently eastward and south-eastward, to disappear finally under a belt of clays, with interbedded sands. These clays and sands, of upper Jurassic age, form the ground under Oxford and Bedford, and in their turn dip under a Cretaceous escarpment, which runs from Flamborough Head through the Chilterns to West Dorset, curving sympathetically with the Jurassic escarpment to north-westward of it. The beds of the soft limestone known as chalk, whose edges are exposed on the face of the Cretaceous scarp, slope eastward and south-eastward, in accordance with the regional tilt, and pass under the thick clays of early Tertiary date, of and upon which London has been built. At several points deep borings for water have pierced the London clay to the underlying chalk. The eastern halves of Norfolk and Suffolk are characterised by a late Tertiary formation, called the Crag, which rests directly upon the chalk, the London clay having apparently been removed from this district before the Crag was deposited. As a consequence of this structure the English plain has a grained surface, like that of sawn timber, and consists of alternating belts which have very various powers of resisting denudation. Owing to the fact that water cannot pass through beds of clay, the rainfall is discharged from clay districts mainly by surface drainage, and the fine substance of the clay is steadily removed by turbid brooks. Sandstones and the softer limestones, on the other hand, allow much of the rainwater to percolate downward, and so greatly reduce the erosive power of the streams. Thus the more porous rocks, by yielding a ready passage to the moisture, preserve a comparatively high resistance to denudation, whereas the impervious clays are rapidly degraded. By these processes, the English plain, formed of more and less resistant belts, has been scoured, like grained wood worn with age, to a ribbed surface of alternating upper and lower strips. Two broad belts of upper ground, formed of Cretaceous and Jurassic limestones, each limited westward and north-westward by a considerable escarpment, sever three lower belts, consisting chiefly of clay-bottomed vales, broken here and there by sandy and even limestone rises. Such rises are Hampstead and Bagshot Heaths amid the London clay, Woburn Heath and Shotover Hill amid the Oxford and Aylesbury clays, and Cannock Chase and Delamere Forest in the wider district of the New Red clay. Owing to the tilt of the beds, the top of the chalk does not stand higher than the Jurassic escarpment, although it is composed of deposits which rest upon the Jurassic rocks. The belts of lower clay ground, having been denuded chiefly by running water, remain a little higher near the sources of the streams than elsewhere. Therefore on the water-parting which divides the Severn and upper Thames from the Trent and Wash rivers, or, roughly, along the line from London to Chester, the ribs of the plain stand in lower relief than further south-westward, by reason of the generally higher level of the intervening softer grounds. To the north-east, however, of the London-Chester line, in East Anglia and in the East Midlands, the whole surface is depressed, so that, as already pointed out, the hills nowhere rise to as much as three hundred feet above the sea, and the intervening lower grounds sink so low that, in the Wash, they have been invaded by the sea, and, over large areas, their constituent clays have been buried beneath marshy flats of alluvium and peat, of which the chief are the Fens round the Wash, the Louth and Grimsby marsh along the Lincolnshire coast, and Hatfield Chase and the ring of marsh round the Isle of Axholme at the head of the Humber. Remnants of New Red and Jurassic deposits, along the shores of Glamorgan and Somerset, prove that the plain once extended where is now the Bristol Channel, and that the break between the Welsh and the Devonian uplands is older than the oldest of the plain formations. Similar reasoning applies to the spread of the New Red strata through the Cheshire gap between the Welsh and Pennine uplands. Moreover, isolated New Red areas exist in the Cumbrian Vale of Eden, in the North Welsh Clwyd Valley, and in the Irish County Antrim, and Jurassic remains have been preserved under the basalts of Mull and Skye. These facts suggest a former continuity of the newer rocks, from Cheshire, through the Irish Sea and the North Channel, into the Hebridean seas, and they reveal the probable antiquity of the break between the Scottish and the Irish uplands. Salt is a characteristic mineral of the New Red deposits, and the distribution of the British salt mines -- in Cleveland, Worcestershire, Cheshire, and Antrim -- is thus dependent on some very ancient events in the history of British geography. It must not be supposed, however, that the conditions of the plain-area have been wholly restful since New Red days. An important fault, striking north and south along the eastern foot of the Malvern and Abberley Hills, has let down the New Red rocks, underlying the Severn Valley at Worcester, so that they end with a broken edge against the Archæan, Cambrian, and Ordovician masses which constitute the little mountain ridge of Malvern. West of the Malverns, as far as the Welsh border, is a district, unique in England, in which the older rocks have presented little resistance to denudation, and have been worn to a lowland. To find equivalents to the Old Red plain of Herefordshire we must go to the Scottish lowlands of similar date in Strathmore, Moray, Caithness, and Orkney. Long after the fracture which produced the Malvern boundary fault, the whole of that portion of the plain which runs eastward from the Devonian uplands to the Weald of Kent was subjected to considerable disturbance, apparently due to pressure from the south. To understand the effect of the rock-movements which took place, it must be remembered that the chalk of Southern England was laid down in continuity with that of Northern France; indeed, the lower chalk must still extend without break beneath the shallow Strait of Dover, a fact which it has been proposed to utillse for the piercing of a Channel Tunnel. Prior to the epoch of disturbance, a thick sheet of chalk, more or less buried under subsequent clays and sands, spread from France, across the site of the English Channel, and over much, if not all, of the English plain. To-day, on the French coast -- north and south of Boulogne -- and right across Southern England, from Dover Cliff and Beachy Head almost to the Mendips, are the denuded remains of a much flattened upfold of these chalk strata, edged by two lines of usually sharp down-flexure. The broad top of the uplifted beds seems to have been slightly creased by minor folds parallel to the main axis of upheaval, and was very gently domed, so as to culminate in the neighbourhood of Tunbridge Wells, where some 3000 feet of rock appear to have been denuded from the summit of Crowborough Beacon, a hill which still rises 800 feet above the sea. Along the northern line of bordering flexure, marked by the chalk range of Surrey and Kent, the strata bend suddenly downward and then. spread into the nearly horizontal floor of the London basin, from under whose clays and sands the chalk emerges again in a long upward tilt, to end in the great Chiltern escarpment already described. Owing to the south-westerly curve of the Chilterns as contrasted with the straighter westerly trend of the North Downs, the London basin narrows westward, and its pointed end is occupied only by the valley of the Kennet. The East Anglian and Kentish shores, following the general lie of the hills, impart a similar form to the Thames estuary. The line of flexure which determines the southern edge of the Wealden uplift carries the chalk down beneath the clays and sands of the Hampshire basin, along whose. axis lie Spithead, the Solent, and the Frome valley of Dorset. Beyond the almost level floor of this downfold, the chalk strata rise once more in a line of very sharp flexure, running west and east through South Dorset into the Isle of Purbeck, and through the Isle of Wight. The grandly upeurving beds, marked by lines of flints, are conspicuous in the white cliffs of Swanage, the Needles, and Culver Point, but the sea has now removed. the southward extension of the raised strata, except in the salient angle of the Isle of Wight, where the chalk top of St. Catherine's Down remains to indicate the flattened character of the original uplift. It is convenient to speak of the more southern of the two belts of chalk upheaval as the Vectian uplift, from the ancient name of the Isle of Wight, while the more northern has been referred to as the Wealden uplift. Both the superficial and the coastal features of the area south of the Kennet-Thames and east of Devon and Somerset, with the single exception of Dungeness, have: been carved by denudation from the great sheet of deposits, which has thus been embossed with two shallow basins expanding eastward and two belts of flattened uplift. While the lower, western end of the Wealden uplift still retains -in Salisbury Plain and North Hampshire -- a complete roofing of chalk, the higher portion of the dome, in Surrey, Sussex, and Kent, has suffered greater degradation. Either by the action of weather, or perhaps by marine erosion during a period of partial submergence, the dome was planed down, so that the strata lying beneath the chalk were exposed. These underlying beds having been affected by the same rock movements as the chalk, the plane of denudation intersected several concentric domes of alternating clays and sandstones, whose cut edges produced a graining of the denuded surface, arranged in oval -- eastward and westward -- concentric rings. The subsequent more rapid destruction of the less resistant rocks has of course left the harder edges salient in relief. In the centre, from Hastings to Horsham, is a hilly nucleus, chiefly of sandstone, known as the Forest Range, which rises to 800 feet. Round this, upon the Weald clay, is a ring of lower ground, incomplete towards the east, because the land has there been breached by the Channel. This is in turn enclosed by a ring, similarly incomplete, of greensand, which is especially prominent to the north and west, where Leith Hill and Hind Head nearly reach 1000 and 900 feet respectively. The thin layer of gault clay produces only a narrow -- as it were incised -- ring of valley, separating the greensand hills from the chalk downs, but it spreads exceptionally into a little plain near Farnham in the northwest. Finally, a chalk escarpment, whose cut face looks inward, frames in the whole district, except to the southeast, along the coast between Beachy Head and the South Foreland. On the French shore opposite -- grasping the little coastal district of exposed sub-Cretaceous rocks, which is known as the Bas Boulonnais -- is a significant remnant of the section that is missing of the ring of chalk escarpment. The details of the topography of Southern England depend very largely on the varying steepness of the dip of the strata along the lines of flexure. In the North Downs, for instance, between Farnham and Guildford, where the dip is very steep, the ridge, known as the Hog's Back, is narrow and comparatively low; but beyond Guildford, where the northward dip begins to take a rather lower angle, the Downs gradually broaden into a belt of upper ground, seven or eight miles wide, with a southward escarpment, from 600 to 800 feet high. Beyond Chatham and Maidstone, the direction of the range changes abruptly from ENE. to SE., and here the chalk surface is again narrow, but it rapidly widens into a terminal cliff-ended plateau, occupying the triangle between Canterbury, Deal, and Folkestone. Thanet is a fragment of chalk upfold, cut short by the waves along the Margate and Ramsgate cliffs, and divided from the main range by a clay-filled downfold, through which ran the former sea-strait of Wantsum, now silted up. The line of flexure, which has produced the North Downs, is continued westward along the northern edge of the plateau of Hampshire, where the chalk roof of the Wealden uplift, still complete between Winchester and Basingstoke, dips down beneath the Tertiary sands and clays of the Kennet Valley of South Berks. As it enters Wiltshire, the flexure begins to take the character of a complete upfold, so that near the point where the three counties of Berks, Hants, and Wilts adjoin, denudation has left a height of nearly 1000 feet at Inkpen Beacon, the highest summit of the chalk. A little further westward the chalk has been worn through along the axis of this upfold, and the underlying rocks have been exposed in a little "weald," known as the Vale of Pewsey. Devizes is here built in a greensand valley, defined on either hand by chalk escarpments. In the Isle of Wight the surface of the Vectian uplift has suffered similar denudation, and the underlying deposits have been exposed between the line of chalk flexure, which crosses the island, and the chalk table on St. Catherine's Down. Thus the English plain consists of two structural systems. (1) Within the Midland quadrilateral, defined by the estuaries of the Mersey, Severn, Thames, and Trent, the topography has been shaped by denudation acting upon rocks grained in curves from north to south-west. East Anglia and Eastern Yorkshire partake of the Midland type of structure. (2) South of the Kennet-Thames, on the other hand, denudation has worked upon material whose graining was determined by the Wealden and Vectian uplifts, striking eastward and westward. The form of the London basin and the outline of the Thames estuary are due to the juxtaposition of these two systems. In the north of Wiits, where the chalk ranges of the two areas converge to form the Marlborough Downs, the strata rise from the narrow downfold under the upper Kennet Valley, on the one hand, northward into the escarpment which overlooks the Vale of the White Horse, a feature of the Midland system, and on the other hand, southward into the escarpment which commands the Vale of Pewsey, a member of the southern system. The floor of ancient rock which underlies the deposits of the plain has been reached by not a few borings for water and coal. The rocks struck are in some cases Carboniferous and in others Old Red or Silurian. It would appear, therefore, that prior to the deposit of the newer rocks, the older formations were not merely folded and faulted, but also planed down by denudation, with the result that along the axes of upfold the deeper strata were exposed, and in the troughs of downfold rocks of somewhat later date were preserved. In other words, the ancient surface, upon which the newer deposits rest, is itself grained like the plain above. The precise pattern of the graining is a matter of deep interest, for it is possible that coal seams may be treasured in some of the downfolds. There are two opportunities of inferring the nature of the underlying rocks in addition to that of actual boring. On the one hand, the structure of the uplands is not likely to change abruptly where it sinks below the sheath of newer deposits; on the other hand, the New Red part of the plain-formations, being relatively thin, is pierced by occasional upthrows of the older rocks. Along a broad belt extending from the Tees to the Mendips, it is therefore possible to describe in general terms the topography of the buried floor. In the coalfields of Durham and the West Riding, the New Red strata rest on the upturned edges of the Coal Measures, but between Leeds and the Tees is an interval in which coal is absent, and the New Red rests directly on the Millstone Grit. It is clear, therefore, that the coal had already been removed from this intervening district when the New Red clays were deposited. The alternative hypothesis that no coal was there formed may be dismissed, on account of the general correspondence of the coal-bearing strata of Durham and of the West Riding, and the detailed evidence that they were once continuous. We must believe, consequently, that with the upheaval of the Pennine fold, forces acting from the north and south threw up a fold at right angles to it, striking east and west, through what is now the North Riding of Yorkshire, and that the Coal Measures were worn off the crest of this fold precisely as they were removed from the Pennine crest. When the New Red rocks were subsequently deposited they rested impartially upon the upturned edges of the Coal Measures along the Pennine flanks, and upon the Millstone Grit forming the denuded axis of this buried ridge. As a consequence, the coal of Durham dips eastward from the Pennine axis and northward from the buried axis, while that of the West Riding dips eastward from the Pennine but southward from the buried axis. On the assumption that in other directions the coal-beds rise against other buried ridges -- perhaps far to the eastward under the North Sea -- we speak of the coal-basins of Northumberland and Durham, and of the West Riding. In the Midland district, west of the Jurassic escarpment, a series of upfolds of the Carboniferous and older rocks radiate from the broad end of the Pennine Range, like the fingers of an outspread hand. In the intervals are shallow basins of New Red clay and sandstone, beneath which recent investigation has revealed considerable areas of hidden coal. The first of the radiating upfolds bears the granitic mass of Charnwood Forest and the Leicestershire coalfield; the second upbends the coal of the Tamworth and Nuneaton field; between these is a New Red basin occupied by the plain of Leicester. The third lifts to the surface the South Staffordshire coalfield and produces the Clent and Lickey ridges; between this and the second is the New Red basin of Warwickshire, whose clays were once covered with Shakespeare Forest of Arden. The fourth is productive of the Wrekin and the Shropshire coalfield; while the fifth is the axis of the North Staffordshire coalfield. A fertile basin of New Red deposits fills most of Worcestershire between the Abberley-Malvern and the Clent-Lickey axes. It is noteworthy that the three counties of Leicester, Warwick, and Worcester, each in turn overlooked by the Jurassic escarpment, should each coincide with a geological basin. The Bristol coalfield resembles on a smaller scale the Durham and West Riding fields, in that it is a rock-basin in the ancient floor, partly buried beneath the newer deposits. The ridge of Carboniferous Limestone through which the Clifton gorge is cut constitutes its western rim, and the Mendip upfold runs to south of it, but the eastern rim is hidden beneath the Cotswolds. As long ago as 1858 Godwin Austin threw out the brilliant suggestion that there might be coal under Southern England, along the line between Bristol and the coalfields of Belgium and Northern France. A recent boring at Dover has proved the correctness of his surmise. Coal has been struck at a depth of about 1100 feet, and a second boring nine miles to northward, on the road to Canterbury, has also reached the Coal Measures. They appear to dip gently from a buried upfold underlying the North Downs, doubtless belonging to the same system as the Mendip upfold further west. It seems, therefore, likely that a belt of several basins, some it may be containing coal, occupies the surface of the buried floor under London, Berkshire, and North Wilts. Should the seams prove to be of adequate importance, it is possible that at no distant date a busy field of industry may extend where now are rural districts unsullied by collieries, and that the unity of the buried floor connecting the Welsh Upland to the Belgian Ardennes, now visible only to the geological imagination, may become patent in the facts of economic geography.		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