THE TERTIARY PERIOD 287 



The Eocene formations are much thicker (1700 feet maximum) 

 than on the Atlantic Coast. Also the deposits are quite distinctly 

 hardened into sandstones, shales, and limestones, with much lig- 

 nite in some places. 



The Oligocene is well represented by the Vicksburg limestone 

 formation and the Apalachicola formation, which latter is very 

 variable but mostly made up of limestones, marls, sands, and clays. 

 These two formations are usually only a few hundred feet thick. 



Miocene strata are represented in Florida by the Jacksonville 

 limestone and Choctawhatchee marl, in the Alabama region by the 

 Pascagoula bluish clay formation, and in Texas by the Oakville 

 limestone formation. A maximum thickness of fully 1500 feet is 

 attained in Texas. 



The Pliocene is represented in Florida by the marine Caloosa- 

 hatchee marl formation, but throughout the rest of the Gulf Coast 

 the Citronelle formation appears to be the only representative of 

 the Pliocene. 



Western Interior Strata. — All Tertiary strata of the western 

 interior are of non-marine origin, and they comprise lake, river, 

 alluvial-fan, and wind deposits, with some volcanic ash and tuff 

 (Fig. 178). 



Of the Eocene deposits, the Fort Union sands, clays, etc. 

 (both lacustrine and subaerial), occur in North Dakota, Montana, 

 and southwestern Canada, where they reach a maximum thickness 

 of 2000 feet; the Wind River variegated shales, together with 

 some sandstones and volcanic ash, are terrestrial (mostly fluviatile) 

 deposits several hundred feet thick in Wyoming; the Wasatch 

 variegated clays, shales, and sandstones, together with some coal, 

 are very largely terrestrial deposits up to several thousand feet 

 thick in Utah, western Colorado, and Wyoming; the Bridger beds, 

 many hundreds of feet thick, are mostly volcanic dust, with some 

 shales, etc., deposited partly on land and partly in shallow lakes 

 in western Wyoming and northern Utah, while the San Juan 

 formation, probably of the same age, is a great volcanic tuff deposit 

 up to 2000 feet thick in Colorado; the Green River shales are 

 lacustrine deposits just to the north and south of the Uinta 

 Mountains; and the Uinta shales, sandstones, etc., are chiefly of 

 terrestrial origin in western Wyoming, northeastern Utah, and 

 northwestern Colorado. 



Oligocene strata, represented by the White River formation of 



