544 D. F. HEWETT 



as well as the long anticlines which coincide with the Bighorn, 

 Bridger, and Owl Creek ranges, were developed after the beds were 

 laid down. The folds are broken by many normal faults of small 

 displacement, none of which appear to pass into the overlying 

 Wasatch beds. 



The term Bighorn Basin Wasatch has long been considered to 

 include the sandstones and alternating olive and red clays of the 

 central part of the Bighorn Basin, where they attain a maximum 

 thickness of about 2,500 feet. These beds include Hght brown 

 and white sandstones, gritty arkose and pale olive, gray, and red 

 clays. The sandstones locally contain pebble zones of re-worked 

 Fort Union materials, with the addition of limestone and granite 

 which are absent or uncommon in those beds. Although bentonite 

 has been reported east of Meeteetse (5), no unaltered volcanic tuff 

 has yet been recognized. The beds are nearly horizontal over 

 large areas in the center of the basin, and although the range 

 along the border is commonly 3° to 10°, dips as high as 20° are 

 known (9). 



The beds of the central part yield a large vertebrate fauna 

 which has been studied from time to time. Only a few invertebrate 

 fossils are known in the beds (5). The recent careful faunal 

 studies of Granger and Sinclair show that the Bighorn Basin 

 Wasatch contains beds that range from "Paleocene" (their Clarks 

 Fork beds) to uppermost lower Eocene (their Lysite or Upper 

 Wind River beds) (7, 8, 9). 



The early work of Eldridge (6) as well as the later work of 

 Fisher (5) showed the presence of a persistent nearly horizontal 

 layer, composed of sandstone and gray and red shale underlying 

 volcanic tuffs in the region between Meeteetse Creek and Owl 

 Creek in the southwest part of Bighorn Basin, and they were con- 

 sidered to be Wasatch. These beds outcrop along the south edge 

 of the Meeteetse quadrangle and the west edge of the Grass Creek 

 quadrangle which have been studied by the writer. In addition 

 to the alternating olive and red shale and sandstones with local 

 chert and quartzite pebble lenses, which are characteristic of the 

 Wasatch deposits of the central part of the basin, there are thin 

 beds of dark carbonaceous shale, carbonized plant remains, and 



