NO. 3 GRAND CANYON FOSSIL FOOTPRINTS — GILMORE 9 



Trail section/ That there is a distinct ichnite fauna in this formation 

 is clearly evident though unfortunately the extreme hardness of the 

 sandstone — and hence its failure to cleave in most instances — makes 

 the collecting of tracks a problem requiring special tools and trained 

 personnel. 



Schuchert's ' description of the Supai as exposed on the Hermit 

 Trail is as follows : 



The lower Supai formation [Supai of modern nomenclature] begins with a 

 thick-bedded and cross-bedded cliff-making sandstone of about 150 feet in 

 thickness. Beneath it are red sandy shales with two bands of sandstones that 

 together have an estimated thickness of 200 feet. At the base of this 

 zone is another horizon of thin flaggy beds with some sun-crack fillings and an 

 abundance of rain-prints of the mammillary kind, interpreted as having been 

 made by long continued rain. Midribs of either ferns or cycadofilices were 

 seen and probably also indistinct feet imprints of amphibians. The trail runs 

 along this zone for about two miles and one has a fine opportunity to study 

 the sediments and to note the abundance of rainprints and a few rill markings. 



The next lower zone is a cliff-making sandstone about 50 feet in height. 

 Then follows one of shales 100 feet thick, that near the top has beds of 

 septaria-like limy concretions embedded in a dark purple sandy mud. * * * 

 associated are also thin zones of intraformational conglomerates with flat and 

 somewhat rounded small pebbles; the shale pieces have blackened surfaces. 



In the field it was estimated that the tracks occurred about 1,800 

 feet below the rim, but upon checking up with Noble's measurements 

 of this section the conclusion is reached that the lowermost horizon 

 would be about 1,767 feet down and the highest track-bearing layer 

 about 1,717 feet below the top. 



As redefined by Noble in 1922 the Supai formation is of Pennsyl- 

 vanian and ? Permian age and rests with possible unconformity on 

 the underlying Mississippian Redwall limestone. The sandstone has 

 its grains bound together by calcareous cement as contrasted with the 

 siliceous binding materials of the Coconino. Noble points out that 

 the thick layers are conspicuously cross-bedded and that the prevailing 

 dip is south as in the Coconino, and further it was noticed that in 

 the majority of instances the trackways were ascending the slopes 

 of the cross-bedding as in the Coconino. 



^ As this paper was going to press, the National Museum received a slab of 

 footprints, presented by Mr. G. E. Sturdevant, which was found by him in the 

 Supai formation at one side of the Bright Angel Trail. In addition to its 

 being an undescribed genus and species, it also records a new locality for 

 tracks in the Grand Canyon. 



It is also worthy of mention that Mrs. G. E. Sturdevant found a small 

 section of the trail of some invertebrate animal in the Bright Angel shale, Cam- 

 brian, a specimen that was also donated to the National collections. 



= op. cit., p. 357- 



