74 SINCLAIR— ADDITIONS TO FAUNA OF [April 24. 



Creek quadrangle, south of the sandhills on the divide between the 

 Niobrara and the North Platte rivers, in draws at or near the heads 

 of Dry Spotted Tail Creek, Spotted Tail Creek and Snake Creek, as 

 follows: Loc. loooA, T. 26 N., R. 55 W., Sec. 31 (N. E. 14) ; Loc. 

 lOooB, same township and range, but in the southeast quarter of Sec. 

 33 ; Loc. loooC, T. 25 N., R. 55 W., Sec. 3 (S. E. >4 to middle of sec- 

 tion) ; Loc. loooD, T. 25 N., R. 54 W., Sec. 2 (N. E. >4). Of the 

 four, Loc. lOOoC, to which the attention of Messrs. Whitford and 

 Earner was called by Mr. John Weir, before my arrival in the field, 

 was particularly productive, yielding some of our best material. 



The Snake Creek beds comprise unconsolidated, water-worn 

 gravels, clean, cross-bedded, round-grained sands sometimes 

 streaked with magnetic, and a mortar-like, gray-white material, 

 sometimes in angular fragments and sometimes in cobbles or boul- 

 der-like masses, resting with marked erosional unconformity on 

 the Middle Miocene Sheep Creek beds. Rolled pebbles of granite, 

 quartzite, etc., indicate water transportation from the crystalline 

 rocks of the mountains farther west, probably some of the sand is 

 windborne, but a large part of the Snake Creek matrix has not 

 been transported far and consists, sometimes, of subangular frag- 

 ments resembling in appearance dried mortar, and, sometimes, of 

 gravels, cobbles, and large masses of more or less indurated clay or 

 silt, evidently represented the harder portions of the Sheep beds 

 through which the Snake Creek channels were cut. Many large, 

 slightly rounded masses of Sheep Creek sediment incorporated in 

 the Snake Creek sands and gravels are quite incoherent and could 

 not have stood thorough saturation with water, not to mention trans- 

 portation to any considerable distance. I think they were derived 

 from the caving of undercut banks along channels incised in the 

 Sheep Creek. Water-worn fragments of silicified wood are com- 

 mon, but are not necessarily remains of a forest contemporary with 

 the Lower Pliocene fauna. Most of it, if not all, is remanie 

 material. 



The stratification is lenticular, water-worn gravels giving place 

 laterally to cross-bedded sands and jumbled masses of clay boulders. 

 Either gravels, sands or mortar-like fragments may rest with clean 

 sharp contact on the eroded surface of the Sheep Creek, the irregu- 



