Ransome.] 



The Great Valley. 



39 1 



This association of deposition and subsidence, discerned at a time 

 when our conceptions regarding the interior of the earth were, if 

 less vague, more primitive than at present, and when the com- 

 monly accepted theory of the earth was that of a thin crust floating 

 upon a molten interior magma, led easily to the explanation brought 

 forward by Herschell,* Babbage.f and Hopkins, % that the subsi- 

 dence was due to a bending downward of the thin crust under the 

 load, and a consequent displacement of the sub-crustal magma. 

 The latter would then most naturally flow under that adjoining 

 portion of the crust relieved of weight by denudation, and cause it 

 to rise". 



When the vast sedimentary accumulations of the United States 

 began to be carefully studied, the same association of deposition 

 and subsidence was even more strikingly shown and on a grander 

 scale. Hall§ in 1859 showed that the sediments, over 40,000 feet 

 in thickness, which were laid down over the site of the present 

 Appalachian region, are all of shallow-water origin, and must have 

 been deposited on a gradually subsiding sea-bottom. He regarded 

 this subsidence as the result of the loading. 



King || arrived at a similar conclusion in regard to the still 

 greater Palaeozoic sediments of the western territories. 



Dutton,T[ in 1879, in a preliminary paper on the Colorado River 

 and plateaus, pointed out that "those areas which have been uplifted 

 most have been most denuded," and says that he has "asked him- 

 self a hundred times whether we might not turn this statement 

 around and say that those regions which have suffered the greatest 

 amount of denudation have been elevated most, thereby assuming 

 the removal of the strata as a cause^and the uplifting as an effect. 



Few geologists," he goes on to say, "question that great 

 masses of sedimentary deposits displace the earth beneath them and 

 subside. Surely the inverse aspect of the problem is d priori 



* London and Kdinb. Philos. Mag., Vol XI (1837), p. 212. 

 t Q. J. G. S., Vol. 3, p. 186. 



X Brit. Assoc. Rept. 1847, p. 73. 



# Palaeontology of N. Y., Introd. to Vol. Ill, p. 69, et. seq. 

 || Exploration of the 40th Par. , Vol. I, p. 732. 



\ Geolog. Hist, of the Colorado River and Plateaus, Nature, Vol. XIX, pp. 

 247-252 and 272-275. 



