W. R. Jillson — Vertehrate Footprints. 57 



occur is about oue foot thick. It is overturned from its orig- 

 inal position above a soft gray clay which has recently been 

 removed at this point by the waters of Elm Creek. Both the 

 impressed clay and the casting sandstone are small and unim- 

 portant members of a long series of interbedded layers of sand- 

 stone and shales. Although a diligent search was made, no 

 exposure of the original upper surface of the clay could be 

 found. Due to the nature of the clay deposit, it is not thought 



Fig. 1. 



Fig. 1. Detailed study showing two series of tracks. Note the lack of 

 heel impressions (horizontal surface ? ). 



that it will ever be possible to collect anything of greater sig- 

 nificance from this locality than these casts. 



The specimen shows a double trail of casts across the slab. 

 In the upper trail the movement was from left to right, and 

 just below one may note the probable return or " back track- 

 ing " of the same individual (fig. 1). Whether this creature 

 was amphibian or reptilian there is no absolute proof, though 

 many small factors point toward the former. Being adapted 

 to a strandline habitat it undoubtedly possessed aquatic ten- 

 dencies, which statement finds considerable support in the size 

 and physical character of the foot impression; A five-toed ani- 

 imal, its feet were apparently almost as broad as long, and this 

 taken into consideration with the close proximity of the foot- 

 prints suggests : (1) a poor adaptation to land locomotion or 

 crawling; (2) probably a more efiicient adjustment to swim- 

 ming or paddling ; and (3) a compromising of these two in a 



