536 Scientific Geology. , 



provisionally under a sixth system. But I possess no data for forming 

 even a conjecture as to the epoch of its elevation. 



In Dr. Richardson's account of the geology of the northwest part 

 of North America, observed during the recent exploring tour under 

 Capt. Franklin, we find him describing a part of the Rocky Moun- 

 tains as composed of four chains, terminated by the northern ocean to 

 the west of Mackenzie's River, and running about S. E. and N. W- 

 They consist of primary rocks: and I mention them here, as a pretty 

 strong indication that a system of elevation with such a bearing exists 

 on this continent. Such a direction, however, is not common in North 

 America in our mountain chains, unless we go as far south as the isth- 

 mus of Darien. 



In comparing the facts which have now been stated in regard to the 

 elevation of our strata, with similar facts developed in Europe, I have 

 been led to conclude that it is a considerably longer period since the 

 elevating force has acted in the United States than in Europe. For 

 we have slight evidence of any extensive disturbance here since the 

 deposition of the strata above the chalk, and not very conclusive evi- 

 dence of such disturbance even so late as the cretaceous period: 

 Whereas, in Europe, several systems of elevation are reckoned of a 

 later date. And this conclusion agrees with the fact that volcanic 

 agency has not yet ceased on the eastern continent, but in the United 

 States, no traces of its action, since the earth assumed its present state, 

 have been discovered. For if I mistake not, the existence of volca- 

 noes in any region, indicates less thickness in the crust of the globe 

 than in other places ; since the melted matter would be forced through 

 the envelope where it is thinest. Accordingly, the only experiments 

 that have been made in the United states upon internal temperature, 

 indicate a less rapid increase as we descend into the earth here, than 

 in Europe; and consequently a greater thickness of the earth's crust 

 on this side of the Atlantic. 



All this would lead to the conclusion that our western continent is 

 older than the eastern : at least that such is the fact with its Atlantic 

 border. Beaumont, however, seems to be of a different opinion. It 

 appears " says he, from the description of Messrs, Vanuxem and Mor- 

 ton, that the ancient level, traced on the flancs of the Alleganies by 

 the tertiary deposits and the alluvia, anterior to that of existing 

 streams, which cover their base, is no longer horizontal. It rises 

 gradually from New England to the Mississippi, so that at the Isle of 

 Nantucket it plunges beneath the level of the ocean ; and from that 



