VII.] ON SOME POINTS IN DYNAMICAL GEOLOGY. 73 



The views of Professor James Hall, as to the relation between 

 great accumulations of strata and mountain-elevations, are cited 

 with approval by LeConte, who, following him, asserts that 

 "mountain-chains are masses of immensely thick sediments." 

 I venture, however, to remark in this connection, that the 

 views both of Mr. Hall and of myself, as his expounder, have 

 as yet been but imperfectly understood either by LeConte or 

 our other critics. Thus they have been defined as " a theory 

 of mountains with the origin of mountains left out " ; while Le- 

 Conte says, " Hall and Hunt leave the sediments just after the 

 whole preparation has been made, but before the actual moun- 

 tain-formation has taken place." Now, in fact, so far as I am 

 aware, neither Hall nor yet myself in my exposition of his 

 views (ante, page 49) has proposed any theory to explain this 

 latter part of the process, that is to say, the uplifting of the 

 deposited sediments which LeConte calls " the actual moun- 

 tain-formation." Hall's contribution to the problem, which, as 

 our author well says, forms " an era in geological science," was 

 to show the relation between mountain-chains and great accu- 

 mulations of sediments ; to illustrate this by the history of the 

 palaeozoic rocks of North America j and moreover to protest 

 against the generally received theory that mountain elevations 

 are due to local upthrusts ; he, to use his own language, " going 

 back to the theories long since entertained by geologists rela- 

 tive to continental elevations." That mountains were the 

 remnants of eroded continental areas had already been taught 

 by Lesley, and long before by Buffon and De Montlosier. It 

 was left for Hall, through a new way, to lead us back to these 

 views ; but the whole theory of the cause of continental eleva- 

 tions was left by him where he found it. In my exposition 

 of his views, I have only endeavored, in addition, to show in 

 what manner a contracting globe and a solid nucleus may be 

 related to the great facts of local subsidence and accumulation. 



I shall not attempt to follow LeConte in his objections to 



the views of Dana and Whitney with regard' to the uplifting 



of mountains, but proceed to notice briefly his own, according 



to which the horizontal thrust resulting from the slow contrac- 



4 



