410 Review of the Progress of 
form their base are to be found beneath their foundations at a 
much lower horizon than in the undisturbed hills of the Missis- 
accumulated thickness of the paleozoic strata which lie buried 
beneath their summits. , 
Mr. Hall has made a beautiful application of these views to 
explain the fact of the height of the Green mountains over the 
Laurentides, and of the White mountains over the former, by 
remarking that we have successively the Lower and Upper Si- 
lurian strata superimposed on those of the Laurentian system. 
The same thing is strikingly shown in the fact that the higher 
mouvtain chains of the globe are composed of newer formations, 
and that the summits of the Alps are probably altered sediments 
of tertiary age. (This Journal, xxix, 118. 
e lines of mountain elevation of De Beaumont are according 
to Hall, simply those of original accumulations, which took place 
then due to a later action upon the earth’s crust, ‘‘ but the course 
of the chain and the source of the materials were predetermined 
by forces in operation long anterior to the existence of the 
mountains or of the continent of which they form a part.” p. 86. 
‘It will be seen from what we have said of Buffon, De Montlo- 
sier and Lesley that many of the views of Mr. Hall are not new 
ut old; it was, however, reserved to him to complete the theory 
and give to the world a rational system of orographic geology. 
He modestly says, ‘‘I believe I have controverted no established 
fazt or principle beyond that of denying an influence of local 
elevating forces, and the intrusion of ancient or plutonic forma- 
tions beneath the lines of mountains, as ordinarily understood 
and advocated. In this I believe I am only going back to the 
views which were long since entertained by geologists relative 
to continental elevations.” p. 82. 
‘he nature of the paleozoic sediments of North America 
clearly show that they were accumulated during a slow pro- 
gressive subsidence of the ocean’s bed, lasting through the pale- 
ozoic period, and this subsidence which would be greatest along 
the line of greatest accumulation, was doubtless, as Mr. Hall 
considers, connected with the transfer of sediment and the vari- 
ations of local pressure acting upon the yielding crust of the 
earth, agreeably to the view of Sir John Herschel. The subsi- 
dence of the ocean's bottom would, according to Mr. Hall, cause 
plications in the soft and yielding strata. Lyell had already in © 
ing upon the results of a cooling and contracting seaof 
od 
os Pee 
