774 GEOLOGY 



The eastern coast. Eocene formations appear at the surface 

 in an interrupted belt from New Jersey to Texas. Their structure 

 is similar (Fig. 499) to that of the Cretaceous, from which they :m 

 separated by an unconformity. The materials of the Eocene were 

 derived largely from the Cretaceous, and subordinately from ol< In- 

 formations farther inland. Clays, sands, and greensand marls are 

 the most common materials of the system, and the conditions of 

 sedimentation were much as in the preceding period. 



The system is more fully represented in the Gulf region than 

 en the Atlantic coast, and is thicker (1,700 feet maximum). It 

 contains much lignitic matter in places, showing that marine con- 

 ditions were not uninterrupted. In Texas, 1 gypsiferous and salif- 

 erous sediments recur at various horizons, though most of the beds 

 are of marine origin, and there are numerous local unconformities 

 in the system, suggesting recurrent changes in the conditions 

 and areas of sedimentation. The principal subdivisions 2 are (1) 

 Midway an; (2) Chickasawan; (3) Claibornian, and (4) Jacksonian. 



The Pacific coast. Marine and brackish-water beds. 3 Marine 

 Eocene formations are wide-spread west of the Sierra and Cascade 

 ranges of California, Oregon, and Washington (Fig. 525), and have 

 considerable development in Alaska. Throughout Washington and 

 Oregon and in some parts of California, the Eocene is unconformal >1< 

 on the Cretaceous (in most places on the Lower Cretaceous = 

 Comanchean or Shastan), while in much of California it is con- 

 formable on the Chico, the division plane between the two beiim 

 indicated by a paleontological hiatus. These relations sugu 

 that just before the Eocene, all of Washington, most of Oregon, 

 and parts of the coastal region of California were land, over which 

 the sea advanced later. The Coastal lands of the time were most ly 

 low, but in southern Oregon and northern California there seem 

 to have been mountainous areas, as also at some points fai-iluM- 

 south. 



1 Durable, Jour. Geol., Vol. II; also Reports of the Texas Geological 

 Survey, and the Austin and Uvalde folios, U. S. Geol. Surv. 



2 Dall, 18th Ann. Kept., U. S. Geol. Surv., Ft. II. This rla^ifir.ition 

 places the Vicksburg in the Oligocene, instead of associating it with the 

 Jacksonian. There appears to be no physicnl reason for this separation. 



3 Arnold, Jour. Geol., Vol. XVII. 



