VALLEYS. 



VAL! 



614 



xnntal displacement It range* accurately with that p4rt of the lake 

 ! Wiudenuere which lie* to the south of the embouchure of the 

 valley. On the eart of Troutbeuk abo, then are dislocation* . 

 connected with the formation of the two striking valleys of Troutbeck 

 and Kentmere. The line of dislocation would seem to put exactly 

 long that port of the tutor valley in which the uiere is situated. 

 Indeed, according to the geologist whose views we are reciting, the 

 existence of any of the larger lakes cannot be accounted for in- 

 dependently of similar dislocations. Taking Wostwator, for instance, 

 iu depth is found to be forty-five fathoms, so that its bottom is pro- 

 bably almost a hundred feet lower than the level of the sea. It is 

 evident that such a basin could not be scooped out by the action of 

 water ; nor is its depth increased by an accumulation of detritus at 

 tin- mouth of the valley, for the river by which its surplus water is 

 discharged cuts into the solid rock. The lake (and its including 

 valley), could only be formed, therefore, by a relative subsidence of its 

 bottom, the strata being relatively displaced on opposite sides of the 

 fault. If, in any such case, this relative subsidence do not extend to 

 the mouth of the valley, or be less there than in the upper part of it, 

 a lak will necessarily be formed. This general explanation will apply 

 to all the lakes of the district 



The lakes, Mr. Hopkins concludes, are thus only " the secondary and 

 accidental consequences of the faults with which they are associated, 

 the primary effects being the valleys in which those Likes are situated ; 

 for. whatever may have been the agency by which the masses once 

 occupying those valleys have been removed, it is easy to see that it 

 wouM act more efficiently along lines of dislocation than elsewhere ; 

 and since the existence of dislocations along the lake valleys may 

 be considered as established, it would seem impossible to avoid the 

 conclusion, that those valleys must themselves have originated in 

 Huch dislocations. We are thus led to conclude that a disloca- 

 tion was produced before the valley began to be formed ; that this 

 led to the formation of the valley by denuding causes ; and that the 

 subsidence which caused the Like was one of the last of that series of 

 repeated disturbances which might occur during the long interval of 

 time which was probably necessary for the completion of the valley. 

 .... This view of the origin of valleys of this kind must be con- 

 cidercd as applicable principally in places nearest the centres or axes 

 of elevation. In other cases they may have arisen altogether from 

 aqueous action ; or, when they originated in dislocations, they may 

 have hod their directions so altered, and their character so modified by 

 den tiding causes, as to retain no distinct traces of their origin." 



From these illustrations, derived from local phenomena, we return 

 to a part of the general history of the subject, in which again physical 

 geography and geology are united, but remain distinct. 



Whatever influence the geological constitution and litliologic.il 

 nature of the strata and rock-masses in which a valley has been ex- 

 cavated, may have upon its form, that form is still independent of 

 what may be termed the geometrical disposition and configuration of 

 those strata and rock-masses. This is equally true of mountains as of 

 valleys. It seems natural to suppose that when a group of strata 

 inclining upwards towards the same line from opposite points form 

 what is denominated an anticlinal, a hill or a mountain should be pro- 

 duced ; and that when a synclinal is formed by the similar meeting 

 in one line of a group of strata inclining downwards from opposite 

 |x>inU, a valley should be the result ; and in many cases such is the 

 fact lint in many owes also the reverse occurs, valleys being situated 

 on anticlinal arches, and mountains consisting geologically of syn- 

 clinal troughs of strata. (Lycll, ' Manual,' p. 67.) Thus it has been 

 recently shown by Sir H. I. Murchison and Mr. Qeikie ('Quart Journ. 

 of UeoL Soc.,' May, 1861), that the enormous mass of Ben Lawers, 

 " like many other mountains in Scotland; as well as elsewhere," 

 actually occupies a synclinal trough, while the deep valley of Loch 

 Tay, like that of the Croat Glen through which the Caledonian canal 

 extends, runs along an anticlinal arch. In this manner the geogra- 

 phical configuration of the land is often quite different from iU 

 geological configuration, or that of its geological elements. In con- 

 nection with this subject, it may be useful to advert to the manner in 

 which the terms in question have come to be employed in i 

 physical geography,* and which has already led to erroneous inferences, 

 a geographer speaks of an anticlinal line, ridge, or axis, be 

 simply means the ridge formed by the meeting of an upward slope 

 and OOtmterslone, or the imaginary line drawn through or along it; 

 and by a iiynclin.il, in like manner, ho merely understands a 

 depression or valley, forim-d l.y the meeting of" a downward slope and 

 counterslupe ; without reference to the geological constitution ,,i the 

 land having such figures. Thus geographical onticlin.ition anil 

 nation (derivatives employed, we believe, for the first time by 

 Mr. Krsyley). are quite different things from the disporition of groups 

 of strata, designated by the geologists as anticlinal and KM 

 Thuo, also, the slope and countenilope may consul of strata, cither 

 X or sloping away from each other; a difference quite iinini- 

 portent in geography, but of great moment in geology. Geogi 



Tbr trrm ar,l;r linal wrm to have been Aral adopted In geogtaphr In Dr. 

 B*' MMmt.r. IsiMlnr, 1 Ixmd., 1134, p. a 10, where It In remarked, that the 

 nnge at moanUlu railed the Karadjrh l>airh, " form, tlie geographical anli. 

 clinal lint between the two great riren Tigris and uphnte, and their 

 nsasrtln tributary tlrranu." 



are often not geologists, and borrow appellations from the science of 

 the Utter, which they une in a sense, quite correct, of their own, Imt 

 at the same time quite different fiom its original one. 



Another ami frequently occurring case of the position of a vnl 

 an anticlinal axis in the following. In certain dome-shaped hills, or 

 elevated regions, which all consider as having been thrust up by a 

 force from below, there is often an elliptical cavity at the summit, due 

 partly to the fracture of the upraised rocks, but still more to aqueous 

 denudation, as they rose out of the sea. The central cavity is called 

 a mllry of elrralioa. It exposes to view the subjacent strata or rocks, 

 and the incumbent stratified mass, the central fiortion of which has thus 

 been removed, dips away on all sides from the axis. The structure 

 and the theory of the production of such valleys were first recognised, 

 and the appellation given to them, by the late Rev. Dr. Buckland, 

 who described a remarkable instance in the valley of Kingsclere, in 

 Berkshire, together with others, all presenting the same features of a 

 valley, circumscribed on all sides by an escarpment, whose com; 

 strata dip outwards from an anticlinal line, running along the central 

 axis of the valley. The most symmetrical valley of clevntion in the 

 I'.riti-h isles occurs in the Woolhope district in Herefordshire, con- 

 sisting of two concentric narrow ranges of hills, almost continuously 

 surrounding a broad, nearly elliptical dome; the lowest and mast 

 ancient strata forming the dome, the incumbent strati the including 

 hills. (Huckland, 'Trans. Geol. Soc.,' series II., vol. ii. ; Murchison, 

 ' Siluria ;' J. Phillips, in ' Mem. of Geol. Survey, 1 vol. ii ; Lyell, 

 ' Principles,' 1853, p. 421.) 



The perusal of the article PAKAU.KI. ROADS in the If ATI -IIAI. II i 

 DIVISION of this work is referred to above (col. 541), as desirable for 

 the student of the history of valleys. Subsequently to the investiga- 

 tions of the eminent observers referred to in that article, and also to 

 those of Professor Agassiz, Sir G. S. Mackenzie, Mr. K. I 'liambers, and 

 others, the structure of the parallel roads of Lochaber has been care- 

 fully studied by a distinguished American geologist, Professor Henry 

 D. Rogers, F.R.S., who occupies, greatly to the advantage of science, 

 the chair of Natural History in the University of Glasgow. The i 



>tudy he stated in a discourse delivered at the Koynl Institution, 

 in London, on March 22nd of the present year (IMli, of which an 

 abstract appears in the ' Proceedings ; ' and in which he states that ho 

 has been led by it to reject all the hypotheses hitherto offered in 

 explanation of the terraces, as inadequate, and to recognise in i 

 phenomena discovered by him, but not before noticed or theoretically 

 considered, a key to the solution of the problem. Of these we will 

 briefly notice the principal, omitting the details, and subjoin the con- 

 clusion at which Professor Rogers has arrived. 



These parallel roods are apparently level, and therefore parallel, 

 " but further instrumental measurements," Professor Rogers remarks, 

 "are necessary before the question of their absolute horizontal/ 

 be regarded as satisfactorily settled ; " on which point, therefore, he 

 seems to be at variance with Mr. Darwin, as well as with Sir T. L. I >iek 

 and Mr. Maclean, by whom, as stated in the former article, they were 

 carefully levelled. 



Each "road," "shelf," or " terrace," according to Professor 1 ; 

 is a nearly level, wide, deep groove, in the easily eroded boulder drift 

 or diluvium [SUIIFACK OK THK KAIITII] which, to a greater or less thick- 

 ness, everywhere clothes the sides of the mountains exhibiting them. 

 They vary greatly in their relative distinctness. With scarcely an 

 exception, each terrace or shelf is most deeply imprinted in the hill- 

 side, and is broadest, where the surface thus grooved has its aspect 

 tloirn the glen, or towards the Atlantic ; and is faintest where the 

 ground fronts towards the head of the valley, or the German Ocean. 

 While conspicuous on the open sides and the westward sloping shoulders 

 of the hills, the terraces ditappear altogether in the recesses or deeper 

 conies which scollop the flanks of the mountains. Each grows usually 

 more and more distinct as it approaches the head of its own S|cial 

 glen, until those of the two opposite sides meet in a round spoon-like 

 point. Each again coincides accurately in level with n 

 sluil" ('i or notch in the hills leading out from its glen into some other 

 glen or valley adjoining. 



The internal structure of the matter composing each terrace c. 

 in an " oblique lamination " or slant bedding of the layers of grav.l, 

 Band, and other sediment which constitute it, such as geologist - 

 liarly recognise as the result of a strong current pn.-hing forward the 

 fragmentary material which it is d> ; i wliirh is held )>y th< m 



to indicate, in the direction towards which the lamina 1 dip, tlir 

 tion toward* which the current has moved. The " dip." or downward 

 slant, is almost invariably up the glen, or towards its head, and ></( 

 dotrn the glen, or towards the Atlantic. 



In all previous hyi>otheses, the agency of ttamtinii water is assumed, 

 either the ocean in its ordinary state of repose, or lakes |>ciit within tin; 

 glens, as explained in the former article. I'.nt to these Professor 

 Rogers uppers the facts, that these level hhclve* are not true marine 

 beaches, <'\l>il>iting not a vestige of any maiim- ci.-.cinc remains, no 

 rippled sands, no shingle, and no sea-cliffs ; that they display, in like 

 manner, a ti" distinctive mark* of 1 



ue organism, neither fresh-water pl.mt not animal having ever 

 1-cen ilJM-ovcred imbedded in th'iu. Nor hon any feasible cause of 

 blockage of the glens at di/brant station* above 

 the waters to the respective heights of the terraces, been assigned ; 



