406 Review of the Progress of 
bonates, chlorids and sulphurets at elevated temperatures, taken 
in connection with the notions above enunciated, and with De 
h 
there already existed a marine fauna. At length, the marine 
limestones predominating, the coal measures come to be of little 
importance, and we have a great limestone formation of marine 
origin, which in the Rocky Mountains and New Mexico occupies 
the horizon of the coal, and itself unaltered, rests on crystalline 
strata like those of the Appalachian range. In truth, Mr. Hall 
observes, the carboniferous limestone is one of the most extensive 
marine formations of the continent, and is characterized over a 
much greater area by its marine fauna than by its terrestrial 
vegetation. 
“The accumulations of the coal period were the last that gave 
form and contour to the eastern side of our continent, from the 
Gulf of St. Lawrence to the Gulf of Mexico; and as we have 
shown that the great sedimentary deposits of successive periods 
have followed essentially the same course, parallel to the moun- 
. tain ranges, we naturally inquire: What influence this accumu- 
lation has had upon the topography of our country, and whether 
the present line ot mountain elevation from northeast and south- 
west is in any way connected with the original accumulation of 
sediments?” Hall's Introduction, p. 66. 
The total thickness of the eee ic strata along the Appala- 
chian chain is about 40,000 feet, while the same formations in 
* Quar. Jour. Geol. Soc., vol. xv, 580. 
? 
