

SURFACE OF THE EARTH. 



SURFACE OF THE EARTH. 



830 



1 . It must be determined by evidence whether the accumulation to 

 be explained happened on the land 'at its present level, or on the bed 

 of the sen. 



1. It must be determined by evidence what was the probable 

 character of the climate in the countries where diluvial accumulations 

 excite attention. 



3. In proposing a general cause, such for example as the movement 

 of glaciers, it must be shown to be adequate to satisfy all the minuter 

 details of the phenomena, and not inconsistent with general limiting 

 conditions established by extensive induction from facts observed in 

 the earth itself, or admitted as parts of general cosniical theory. 

 [REFRIUERATION OF THE GLOBE ; and, in NAT. HIST. Div., GEOLOGY 

 and SUBMARINE FOHKSTS.] 



The determination of the cause of the diluvial accumulations is of 

 the highest importance in geological theory. It is impossible to doubt 

 that to the game cause must be ascribed many considerable modifica- 

 tions of the pre-exutent surface of the land. If, abstracting our 

 attention from the accumulated deposits which conceal the stratified 

 and other rocky masses in the crust of the earth, we look at the actual 

 f its surface, there appears little that is even difficult of explana- 

 tion by the application of known and real causes* The relative areas 

 of sea and land ; the peculiarities of outline of continents and islands ; 

 the directions of mountain-ranges, and remarkable vales and plains ; 

 the individual features of hills and valleys ; the degree in which the 

 land is wasted in some quarters and augmented in others ; and the rate 

 of change which may take place in these respects ; all this may be 

 satisfactorily referred to subterranean and submarine disturbances of 

 different periods, to the effects of the sea upon the land when the land 

 was not at its present level above the water, and to the operation of 

 the atmosphere, rains, rivers, and inundations. 



From this large field of research we shall select for brief illustration 

 the outlines of land and sea, the directions of high and low ground, 

 and the individual features of hills and valleys. The few examples 

 needed will be drawn from the British Isles, but the explanations are 

 of general application. To render the article, as reproduced in this 

 work, more accordant with the actual state of geology, illustrations of 

 other parts of the subject are now added, some from foreign countries, 

 )>ut : (,niTal application equally with the former. 



Much of the irregularity of outline, on a large scale, of the British 



Islands depends on the form in which the ancient bed of the sea was 



elevated into dry land. Thus the line of the Hebrides, the prominent 



ports of Caithness, of Aberdeen-hire, and of Argyleshire, are on axes of 



upward movement of the primary strata ; while the Great Caledonian 



from Fort William to Inverness, and the great basin of the 



Forth and Clyde, are in axes of depression of the strata. This latter 



. is margined on the south by the great axis of elevation of the 



( inll.iway and Lammermuir hills, reappearing beyond the Irish Channel 



south of Belfast, as the Argyleshire chain is resumed in Donegal The 



Isle of Man, the promontory of Llcyn in Caernarvonshire, the cast 



and west ridges and hollows of the strata which reach the sea in South 



Wales and North Devon, give to Pembrokeshire, Glamorganshire, and 



ti remarkable and detailed alternations of promontory and 



bay. The Isle of Wight is formed on an axis of elevation from the 



Needle* to Culver Cliff; while north of it are the axis of depression of 



the Solent, the axis of elevation of the wealds of Sussex, and the axis 



: ression of the estuary of the Thames. 



Inland, the same ridges and hollows, and others of as great import- 

 ance, produce continuous chains of hills the North- Western Highlands, 

 the Crampiins, the Lammennuir range of hills, the Wicklow moun- 

 tains, the Snowdon mountains, the Berwyn, and Malvern hills, and mul- 



of other narrow tracts of elevated land. Great fault*, elevating 



u*ung one portion of a natural district, leave marks of inequality 

 on the surface. Thus the great Pennine faults, ranging from New- 

 castle to Brampton, and thence to Kirby Lonsdale and Settle, occasion 

 differences of level in the ground of 1000 and 2000 feet for a length of 

 I" 11 miles. 



In all cases, and in every country, it appears that, notwithstanding 

 the operation of later agencies, the main features of the surface of the 

 Land are due to the positions in which subterranean movements left 

 the displaced masses of rocks. But the operation of subsequent 

 agencies is distinctly traceable in modifications of these features on the 

 sea-coast, and in the interior of every country. 



The surface of the land has been tuultd, and as the various stony 

 and earthy masses which come to the surface have unequal compact- 

 ness, and are unequally capable of resisting the chemical and mechanical 

 agencies which originate in the varying heat and moisture of the atmo- 

 sphere, we find in consequence a multitude of irregularities, both on a 

 large and small scale, directly related to the properties of the rocks. 

 On the sea-coast sonte parts are known to be wasted (as the coasts of 

 Sheppey, Dunwich, and Bridlington) even rapidly, one or several yards 

 annually on the average ; others seem almost unchanged by a thousand 

 yean of storm and tempest, as the " \Vnnn'-! Head ; " and some 



rnble tracts of new land have been added to the shores of 

 Lincolnshire, along thn banks of the Thames, and by the side of the 

 Severn. 



The line of coast from the Tyne to the Humber is instructive in 

 thii resjiect. The prominence'! on the Durham coast, ending with 

 Hartlepool, are guarded by magnesian limestone, and the estuary of 



ARTS AKD SCI. DIV. VOL. VII. 



the Tees is excavated in red marl and lias clays. The peak near Robin 

 Hood's Bay, Scarborough Castle Hill, Filey Brig, and Flamborough 

 Head, are all promontories of hard rocks; but Robin Hood's Bay, 

 Scarborough Bay, Filey Bay, and Bridlington Bay, are all excavated 

 and wasted in clays of the liassic, oolitic, and diluvial periods. The 

 interior of the country shows similar effects on a grander scale. The 

 great vales and plains of England, in parts the least influenced by 

 subterranean disturbances, are by no means the excavated paths of 

 rivers, nor are the great ranges of hills the separating summits 

 between such rivers. The plains and vales are lines of soft and 

 perishable strata, and the crests which divide these vales are ranges of 

 harder rocks. A transverse section of the English strata shows always, 

 both on a large and small scale, this important fact (see fig. 1), and 



Fig. 1. 



Fig. \ shows the relatively prominent parts in a line of section across the 

 secondary strata. 1, being chalk ; 2, lower green-sand ; 3, coralline oolite 

 and calcareous grit ; 4, cornhrash ; 5, forest marble ; 6, great oolite ; 

 7, inferior oolite; 8, marlstone ; 9, lias limestone. The intervening 

 hollows are uniformly argillaceous. 



every well-shaded topographical map, coloured geologically, demon" 

 strates the extent of its application in explaining the irregularity o^ 

 surface. The chalk hills, oolitic hills, &c., alternating with vales of 

 clay, in all the southern and eastern parts of England, give to those 

 parts characters far more important than the undulations connected 

 with river channels. 



Similarly, hills and valleys, in which rocks of unequal power of 

 resisting watery action appear, show the force and continuity of this 

 action by the prominence of the hard rocks and the excavated surfaces 

 of the softer masses. Thus, in fig. 2, we see on the breast and edges 



Fig. 2. 



Fig. 2. Aspect of a mountain consisting'of carboniferous limestone, shale, and 

 sandstone ; the limestone bands (marked 1} project remarkably, and, where 

 they cross a valley, make "waterfalls. 



of a hill composed of limestones, sandstones, and shales, the especial 

 prominence of the limestones ; and where these cross a valley, each 

 limestone edge is the place of a waterfall. By studying in such valleys 

 the manner in which the actual stream wastes the rocks, we can easily 

 assure ourselves of the truth of the general explanation offered above. 

 In fi'j. 3 is a section of a waterfall, showing the edge of limestone (a) 



Fis. 3. 



Fig. 3. The side view of a -waterfall, where the stream falls free of the rock, 

 and causes excavation in the subjacent shales. 



over which the water falls, and under it a bed of sandstone (6) little 

 wasted, but at the bottom a body of shale which has perished by the 

 dampness and spray, and is excavated in a remarkable manner. 



Just such an action is observable on similar cliffs by the sea, and in 

 each case the same effect follows : the falling of the hard rock at top 

 from want of support below. Thus the situation of a waterfall is daily 

 displaced, and is moving up the stream, as the Falls of Niagara and 

 Hardrow Force are known to have done. (Lyell, ' Principles of Geology.') 

 Into all these effects of waste on the earth's surface rain enters for 

 something important. Few surfaces of rock are altogether exempt 

 from chemical changes dependent on atmospheric variations ; all are 

 more or less liable to perish with rain, frost, and watery movements ; 

 and thus the individual features of hills and valleys, the ranges of high 

 and low ground, and the outlines of land and sea, appear to be effects 

 impressed by subterranean movements and fractures of the earth's 

 crust, modified by the action of the sea on materials of unequal 

 resisting power, while they were below, and while they were rising 

 through its waters, and by the subsequent mechanical agencies of 

 rivers, rains, and chemical forces excited by atmospheric variations. 

 [GEOLOGY, in NAT. HIST. Div.] 



Mr. O. Poulett Scrope, M.P., F.R.S., the author of some precious 

 contributions to igneous geology, of the most original kind, but which, 



3 o 



