576 



HISTORICAL GEOLOGY 



except in the form of footprints. Since these sediments were depos- 

 ited in more or less isolated basins, the work of correlating them with 

 each other, and especially with the marine deposits of the Atlantic 

 and Pacific, has been difficult. 



The Eocene was an epoch of great coal formation, especially during 

 the earlier portion (Fort Union). The great lignite deposits that 



cover one half of 

 North Dakota were 

 formed at this time, 

 as were also exten- 

 sive areas in Wy- 

 oming and Montana. 

 The Eocene was 

 brought to a close by 

 crustal movements 

 of some importance 

 which, on the Pacific 

 coast, resulted in the 

 draining of certain 

 areas and the lower- 

 ing of others to below 

 sea level. In the 

 same region some 

 mountain ranges 

 (Klamath) were again 

 bowed up to some 

 extent, and others 

 (Coast Ranges) began 

 their development. 

 In the Great Plains 

 region the changes 

 were such as to bring 

 about aggradation 

 where degradation 

 had formerly prevailed. The interior mountain region of the west 

 was elevated and drained, and in subsequent epochs was not a region 

 of extensive deposition. The eastern coast remained much as before. 

 A narrow strip of land was added to both the Atlantic and Gulf coasts. 

 Eocene of Other Continents. — The evolution of the continents of 

 Europe and Asia was not so far advanced at the beginning of the 



Fig. 529. — Map showing the probable outline of 

 North America during a portion of the Eocene. The 

 continental deposits are shown in solid black. (Modified 

 after Schuchert.) 



