OTOLOGY. 



QEOLOOY. 



t their pleasure the position of the axis of rotation of the earth, few 

 difficulties need (top the career of speculation ; but the earth is a 

 spheroid of revolution, and if the attraction of the heavenly bodies in 

 the various positions which it takes with regard to them does not 

 disturb its axis of figure, neither can it be thought that the volcanic 

 fever of its surface can so alter the interior densities as to cause any 

 sensible change in this respect. 



But that the bed of the sea may have mink, that other continents 

 than ours may have fallen below their ancient level, may be assumed , 

 as readily as the rising of the existing land, but with this restriction, 

 that the sinking of the bed of the sea requires to be far greater than 

 the rising of the land, because three-quarters of the globe are eovered 

 by water, and thus a small difficulty is overcome by introducing a 

 greater. 



Frequently however this dependence of the form of the existing 

 land upon the ranges of mountains is disguised by the extent of com- 

 paratively plain country which separates the mountains from the sea. 

 Thus, all the eastern half of England might seem to have its form 

 independent of the narrow ridges of the western mountains ; ami it 

 is but a vague relation which links the Baltic, the Black Sea, and tin- 

 Caspian to the Hare, Saxon, Carpathian, Caucasian, and l'r.!i .u 

 chains. In these and many other cases it is necessary to admit tlmt 

 the general level of the sea has subsided, or that large tract* of land 

 have been raised gradually, or by successive movements round tin- 

 mountains, which in earlier times were uplifted by more violent 

 effects. The diagrams, fgt. 2 and 3, illustrate the fact of the ; 

 slope of the English strata from the western mountains; but tin- 

 cannot be explained by the violent elevation of these mountains, fur 



I'ig. i.o, Red marl ; 6, lias limestone ; c, lias days ; d, lower oolite formation ; e, Oxford clay ; /, middle oolite formation ; y, Klmmcridgc clay ; 



A, upper oolite. 



Finally, on turning 

 to the phenomena 

 connected with moun- 

 tain chains, it is per- 

 fectly certain from 

 the position of the 

 strata often vertical 

 or contorted in the 

 sides of chains, highly 

 inclined near them, 

 and gently sloping at 

 greater distances 

 that these rocks have 

 been displaced by an 

 elevating force acting 

 from below. The 

 direction of the force, 

 the geological time 

 of its occurrence, its 

 sudden or gradually 

 accumulated inten- 

 sity, and many other 

 characteristic circum- 

 stances, can be deter- 

 mined ; and upon the 

 whole no doubt re- 

 mains that elevating 

 movements have 

 raised the hind, and 

 there is no reason to 

 deny that depressing 

 movements may have 

 sunk the bed of the 



Fig. 5. a, t>, c, d, e, f, have the same meaning as in Fig. 4 ; 1 1 1, m m m volleys which descend with the 

 slope of the strata, here supposed to dip south ; XN, and F, longitudinal valleys, or such u run parallel to 

 the outcrop of the strata ; T, a transverse valley, uniting the longitudinal one?. 



Throughout all the 

 globe the outlines of 

 land and sea depend 

 principally on the dis- 

 position of mountain 

 chains and groups, 

 which in every in- 

 stance yet known are 

 certainly shown to 

 have been raised by 

 mechanical agency, 

 generally with a de- 

 gree of violence so 

 gnat as to require 

 the supposition of 

 great and general ex- 

 citement of the sub- 

 terranean forces of 

 heat America, for 

 instance, derives its 

 form from the chains 

 of the Andes and 

 Rocky Mountains, 

 the littoral range of 

 Brazil, the Allegha- 

 nies, Ac., mountains 

 probably of very unequal antiquity. 



Fig. 0. The letters have the same signification at In Figi. 4 and t 



rf i (. v . The Ghauts define the western 

 t India, as the Atlas mark the north-western border of Africa ; 

 * Pyrenees and Sierras give the form of .Spain; the Cornish, 

 Welsh, Cumbrian, Lammermuir, -and Grampian ranges explain the 

 figure of England and Scotland. 



ended (if, indeed, it bo 

 epochs. Thus, the Alps, 



this happened princi- 

 pally before the de- 

 position of the coal 

 strata. A large area 

 round these moun- 

 tains has since been 

 gained from the sen 

 by more gradual 

 changes of level. 



Similar phenomena 

 present themselves in 

 detached areas nil 

 over the world; but 

 in very unequal de- 

 grees, and with un- 

 equal differences of 

 level above the ocean, 

 even in neighbouring 

 tracts. It appears 

 therefore more pro- 

 bable that particular 

 regions have risen 

 round the same points 

 and lines which once 

 experienced a violent 

 upward movement. 

 There is no reason to 

 deny that the ocean- 

 level may hare been 

 somewhat lowi-n-d 

 by the subsidence 

 of a part of its bed ; 

 but it has been al- 

 ready shown that no 

 reasonable (perhaps 

 no possible) sinking 

 of theoccan-bed could 

 explain the pheno- 

 mena of the desicca- 

 tion of oven the 

 flatter parts of the 

 laud. 



The interior f< a- 

 tures of every coun- 

 try, in like manner, 

 depend upon recog- 

 nised geological agen- 

 cies. The unequal 

 elevation of mountain 

 ranges above the sea 

 ia a phenomenon 

 which will be found 

 of great importance 

 in geological theory. 

 It appears to bo true, 

 at least in Km 

 that the most ele- 

 vated chains of moun- 

 tains are those whose 

 elevation was not 

 yet ended) until the tertiary or later 

 which bear on some of their heights 



