NO. 9 GRAND CANYON FOSSIL FOOTPRINTS GILMORE 39 



by Hitchcock who apphed to one the name HopIicJiiius cquus. Al- 

 though unable to reach any conclusion as to the class of animals to 

 which they might be attributed, Hitchcock was of the opinion that 

 they were true tracks and not discolorations. He attempts to show 

 that they occurred in regular sequence and were depressed below the 

 general surface level. Hay ' remarks : " It is doubtful whether or 

 not this genus of foot marks was produced by a vertebrate animal." 



Sir William Jardine described some hoof-like tracks from the 

 New Red Sandstone of Scotland under the name ChcUchmis gigas^' 

 While these have the same hoof-like shape without the appearance 

 of toes or claws, they do show a distinct pace and uniform alternate 

 progression. 



May it not be that the Supai markings are stains resulting from 

 the decay of some gelatinous medusa-like animals that were stranded 

 on a sandy beach ? 



' Hay, O. P., Bull. 179, U. S. Geol. Surv., 1902, p. 546. 

 ^ Ichnology of Annandale, 1853, p. 9, pi. i. 



