of 



til 



t 



) 



e 



liioli ij 

 iaiii 



r 

 I 



> 



( 



^^i 



ts. 



e 



iniforin 



caused 

 bems 

 Jiequa- 

 iwer of 

 ?tion of 

 r then 



F 



I 



}l}eDO i. 



lu 



LUT 



ent; 



appose 

 idnallj 





lie 



«ea 



tbeO) 



f 



■M 



\(i\h 



uic 



or 





XXXIIJ 



I PEESEEVATION OF BALANCE OF DRY LAND. 239 



hills and momitains composed of stratified deposits, that 

 such inequalities of the surface would have had no existence 

 if water, at some former period, had not been labourino- to 

 reduce the earth's surface to one level. 



But, besides the transfer of matter bj running water from 

 the continents to the ocean, there is a constant transporta- 

 tion from below upwards, by mineral springs and volcanic 

 vents. As mountain masses are, in the course of ao-et^ 

 created by the pouring forth of successive streams of lava so 

 stratified rocks of great extent originate from the deposition 



lime, and other 



miner 



which springs are impregnated. The surface of the land, 

 and portions of the bottom of the sea, being thus raised, the 

 external accessions due to these operations would cause the 

 dunensions of the planet to enlarge continually, if the amount 

 of depression of the earth's crust were no more than equal to 

 the elevation. In order, therefore, that the mean diameter 

 of the earth should remain uniform, and the unevenness of 

 the surface be preserved, it is necessary that the amount of 

 subsidence should be in excess. And su< 

 of depression is far from improbable, on mechanical prin- 

 ciples, since every upheaviner movement 



■edomina; 



must 



diminution of its density. 



mass 



must 



matter 



mineral springs, or from the contraction of argillaceous 

 masses by subterranean heat ; and the foundations having 

 been thus weakened, the earth's crust, shaken and rent by 



If we embrace 



must 



im 



mor 



subsidence than elevation, the average depth to which former 

 surfaces have sunk beneath their original level must exceed 



the 



mar 



sea. 



If, for 



exam 



marine strata, about the 



age 



of our chalk and greensand, have been lifted up in Europe 



more 



some hmidreds, we may 



parts of the surface, which existed when those strata were 



4 



