1913-] LOWER PLIOCENE SNAKE CREEK BEDS. 75 



larity of which is increased by land sHding occuring along the sides 

 of the draws where the exposures are found, but much of it is due 

 to changes in the slope of the channel-beds in which the Snake 

 Creek deposits accumulated. Upward, the formation merges into 

 wind-blown sands and silts which cover the prairie top, and it is 

 not always possible to distinguish between them, as bones sometimes 

 oecur in the lower layers of the sand above the level of the typical 

 Snake Creek gravels. 



Exposures, when found, are along the sides of the draws which 

 have cut down through the Snake Creek beds into the under- 

 lying Sheep Creek, and are usually more or less obscured by wind- 

 blown sand overgrown with grass and weeds, so that little in the 

 way of fossils can be seen at the surface except an occasional weath- 

 ered bone fragment on the bare spots between grass clumps. Occa- 

 sionally, a larger ungrassed area of sand and pebbles may show a 

 few horse teeth, a jaw fragment or two or the ends of some broken 

 limb bones. All collecting was done by stripping off the surface 

 sod and exposing the Snake Creek-Sheep Creek contact wherever 

 the greater abundance of gravel and bone fragments suggested the 

 presence of a productive "pocket" or lens of bone-bearing gravel. 

 If the preliminary prospecting seemed to warrant further excava- 

 tion, a large area was cleared and the bank cut back to a vertical 

 face which was worked by undercutting at the level of the contact 

 just mentioned. This was kept up until the productive gravel was 

 exhausted or the repeating caving of the heavy top burden of sand 

 made further work both laborious and dangerous. 



The bones are remarkably well preserved, mostly black or of a 

 dark color, and occur in both the gravels, sands and mortar-like 

 conglomerate, becoming scarce as the sand gets clean or the number 

 of clay boulders and cobbles increases. They are all more or less 

 abraded, sometimes by water wear, at other times manifestly by 

 wind-blown sand,^ and vary in character from rolled bone pebbles 

 to complete skulls. Hardly ever is there association of adjacent 

 parts. Occasionally a remanie fossil, washed out of the Sheep 



.-The type skull of Protolabis princetonianus sp. nov. was found in soft 

 sand, lying on the left side with the front of the skull tilted downward. The 

 arch and back of the skull on the upper (right) side are pared down to a 

 common level in a manner suggesting sand-blasting. 



