132 



HISTORICAL GEOLOGY. 



Fig. 134 (continued). 



Periods 



Epochs and Sub-Epocfis. 



Pleistocene, or Post-tertiary. 



Pliocene. 



Miocene. 



Eocene. 



f Upper or White 

 Upper Cretaceous. < Chalk. 



( Lower or Gray. 



Middle Cretaceous (Upper Green-Sand). 

 Lower Cretaceous (Lower Green-Sand). 



Wealden. 



Upper <Wlt fc { p ^*J*X." d 



Middle 00lite.{^l ; «§. 4y 



3== Lower Oolite. 



Stonesfield. 

 Inferior Oolite. 



Upper Lias, 

 Marlstone. 

 Lower Lias. 



Keuper. 



Muschelkalk. 



Bunter-sandstein. 



In the figures and maps introduced beyond, the numbers are used 

 as in the above tables : 1 standing for the Azoic ; 2 for the rocks of 

 the Potsdam period, 2 a for the Potsdam epoch, 2 b for the Calci- 

 ferous sand-rock ; 3 for rocks of the Trenton period, 3 a, 3 b, for the 

 epochs of this period ; and so on. 



The following map of the United States east of the Rocky Moun- 

 tains exhibits the geographical distribution of the rocks of the several 

 ages, — that is, the regions over which they are severally the surface- 

 rocks. 



The Silurian is distinguished by heavy horizontal lining ; and the 

 dotted line over the Silurian area divides the Upper Silurian (u) 

 from the Lower Silurian (7). 



