774 



INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



L 10. CASCADE RANGE AND YAKIMA VALLEY, WASHINGTON. 



The Eocene of the upper Yakima Valley comprises sediments and igneous rocks 

 which in order from older to younger are the Swauk formation, Naches forma- 

 tion, Kachess rhyolite, Teanaway basalt, gabbro, Roslyn formation, and Manastash 

 formation. The following descriptions are condensed or quoted from those of 

 George Otis Smith r""'^^^^ 



The Swauk formation consists of conglomerate, sandstone, and shale, which vary greatly 

 in character from place to place. At the base there is usually a conglomerate or arkose derived 

 directly from the older rocks and composed largely or exclusively of their material. Arkose 

 sandstones and carbonaceous shale make up the greater part of the formation. The thickness 

 is 3,500 to 5,000 feet but varies with inequaUties of the underlying surface, which are considerable. 

 The shales contain abundant and well-preserved fossil leaves, which are regarded by Knowlton 

 as of Eocene age. 



The Roslyn formation occurs in a small basin in the upper Yakima, where its extent and 

 structure have been well determined in the development of the coal mine opened upon its prin- 

 cipal coal bed. The greater part of the formation consists of massive sandstones, with which 

 fine-grained clay shales are interbedded. The thickness is approximately 3,500 feet. The 

 included flora is quite distinct from that of the Swauk formation and has Miocene affinities, 

 but, though evidently younger than the Swauk, it is considered to belong in the Eocene. 



The Manastash formation is the latest Eocene sedimentary deposit known in the Yakima 

 Valley. It rests directly upon the pre-Mesozoic schists, with a weU-developed basal conglom- 

 erate,' and consists ,of about 200 feet of sandstone and shale. But two small areas are known, 

 and they might readily be confused with other similar sandstones, which, however, do not have 

 the flora that the Manastash contains. It has been described by Knowlton, who states that 

 none of the species occur in the Roslyn or Swauk formations. They are correlated with species 

 found in the Florissant beds of Colorado and at Corral Hollow, California! 



The Naches formation is composed of interbedded sandstone and basalt, the sedimentary 

 rock predominating in the lower and the volcanic in the upper portion. * * * ■^q occur- 

 rences of the Naches formation are known outside of the Snoqualmie quadrangle. 



Since the Naches and Swauk formations are not found in juxtaposition, there is lack of direct 

 stratigraphic evidence regarding their relative ages. It is noteworthy, however, that they have 

 similar relations to both the older and later rocks, a fact which suggests that they may bo 

 nearly contemporaneous. The evidence afforded by fossil plants confirms this view. 



L 12. BIGHORN BASIN, WYOMING. 



For the southwest side of the Bighorn Basin Woodruff "" determined the follow- 

 ing section of the Tertiary : 



Section of coal-hearing and associated rocks exposed along Shoshone River near Cody, Wyo. 



System. 



Tertiary. 



Cretaceous, 



Formation. 



Wasatch formation. 

 Unconformity - 



Fort Union formation. 



-Unconformity (?)- 



Laramie (?) formation. 



Thickness 

 (feet). 



3,100 



Characteristics. 



Various colored shales interbedded with sandstone and 

 conglomerate. 



Gray to drab sandy shale and tan-colored massive sand- 

 stone. In the lower part of the formation conglom- 

 erates occur at intervals through 1,000 feet of strata. 



[See p. 684 for the Cretaceous section.] 



