6 STRATIGRAPHICAL GEOLOGY. 



development of enormous Triassic and Cretaceous deiDosits between the 

 long Paleozoic strip from Texas to the Arctic zone and the Rocky Moun- 

 tains, while along the latter region we fail to find the former groups to 

 any very marked extent, as would be expected were the western outcrops 

 steadfastly elevated at the same period with the eastern. If we may say 

 that the North America of Triassic times extended from Greenland and 

 the Atlantic ocean to Texas, we may also say that, by the close of the 

 Mesozoic, she had annexed to herself, by means of a specially constructed 

 causeway, the whole of the Rocky Mountain series of islands. Possibly 

 the genius of the continent is now looking forward to a similar absorp- 

 tion of the West India islands, through the filling up of the straits of 

 Florida and the intra-insular spaces. 



TJiird. There were two promontories extending south-easterly from the 

 early continent, — one the w^ell-known Adirondack area, and the other the 

 metalliferous district near Lake Superior. The latter sent off a promi- 

 nent spur also towards the Laramie Mountains of Wyoming, projecting 

 eastwardly from the Rocky range. In fact, it is not unlikely that a bridge 

 connected these projections of land through the Black Hills during mid- 

 dle Paleozoic times. 



FoM'tJi. The immense areas and the enormous thicknesses attained by 

 the Eozoic formations, especially in comparison with the later groups, 

 suggest that the earlier rocks have yet revealed to us very little of their 

 history. The later formations occur in comparatively thin incrustations, 

 easily studied and identified through fossils. The earlier groups are 

 much more difficult of identification, are best developed in the thinly 

 settled or absolutely wild districts, and hence have not yet assumed that 

 importance in stratigraphical columns which they are destined to receive 

 in the future. We trust, therefore, that geologists will not be too hasty 

 in deciding against the attempts of this volume to set forth the reality 

 of several new subdivisions in the Eozoic column of the Atlantic system. 



The Atlantic Area. 



In the chapter upon Topography, vol. i, p. 170, mention is made of 

 two sections of the mountains along the Atlantic, the first culminating 

 in western North Carolina, the second in New Plampshire. By referring 

 to Fig. I, I think it will appear that the Atlantic system should be 



