FOSSILS OF THE FOX HILLS SANDSTONE 401 



mation, especially in the region west of the Black hills. The following 

 fossils obtained from the Fox Hills sandstone near the Bighorn moun- 

 tains were determined by Mr T. A . Stanton : 



Cardium speciosum M. and H. ; Avicula lingaiformis Ev. and Sh. ; A. ne- 

 brascensis Ev. and Sh. ; Ostrea glabra M. and H. ; Liopistha (Cymella) 

 undata M. and H. ; Leptosolen, n. sp. ; Cylichna (?) sp. ; Baculites, sp. ; 

 Modiola, sp. ; Prima lakesi (?) White ; Leda n. sp. (?) ; Thracia subgracilis 

 Whitfield ; T. subtortuosa M. and H. ; Lunatia subcrassa M. and H. ; 

 Sphxriola (?) cordata M. and H. ; Tellina equilateralis M. and H. 



LARAMIE FORMATION 



The wide expanse of plains lying between the foothills of the Bighorns 

 and the Black hills is occupied by Laramie and overlying formations. 

 The formation lies in a broad, flat bottomed basin, with steep dips on 

 the west side on the slope of the Bighorn uplift. The thickness of the 

 beds lying in this basin is not definitely ascertained, but it appears to 

 be several thousand feet. The lower members are undoubtedly Laramie, 

 but the upper ones probably extend into the Fort Union formation. The 

 Laramie rocks are sandstones, sandy shales, and shales, with numerous 

 beds of lignite. At the base there is usually a very characteristic mem- 

 ber consisting of alternating shales and thin bedded, rusty sandstone. 

 This in the northern portion of the region is succeeded by a conglom- 

 erate containing pebbles of limestones and of the characteristic flat pebble 

 conglomerate of the Deadwood formation, derived from the mountains 

 westward and indicating that there was uplift in the region in early 

 Laramie times. This conglomerate begins west of Sheridan and extends 

 southward to Crazywoman creek. The conglomerate is succeeded by 

 sandstones and shales, with coal beds, which occur at various horizons. 



Laramie Range 



general relation of the formations 



South of the Bighorn uplift there is a transverse syncline, and it is 

 not until the north end of the Laramie range is reached that the older 

 rocks again appear. In this range some of the formations present fea- 

 tures different from those in the uplifts to the north and east. The 

 Cambrian appears to be present, but it is thin and soon disappears, and 

 to the southward there is a gradual overlap of the Upper Carboniferous 

 rocks onto the granites of the main uplift. The Mesozoic rocks do not 

 exhibit much change. The geology of the southern part of this region 

 was outlined by the Fortieth Parallel Survey, and F. V. Hayden de- 

 scribed a few details at the northern end of the range. Along portions 



