NO. 9 GRAND CANYON FOSSIL FOOTPRINTS — GILMORE 3 



years, if that were possible, so stupendous as to be almost beyond 

 human comprehension. 



It is hoped that the object lesson so graphically taught by this 

 unique exhibit may serve as an example to stimulate the preparation 

 and preservation of other natural phenomena to be found in our 

 government-controlled parks, monuments, and reservations. 



GEOLOGICAL OCCURRENCE 



The Coconino sandstone of the Hermit Trail in w^hich these tracks 

 occur is considered Permian in age.^ In this section it has a total 

 thickness of 350 feet, but, so far as known, footprints are found 

 only in the lower half. The greater part of the material here de- 

 scribed was collected from one level about 150 feet above the base 

 of the formation (see fig. i). A few tracks were found at a level of 

 20 feet above the base, the lowest point at which imprints appeared. 

 Between these two extremes, tracks were observed at several levels, 

 and there is reason for beliefving that they may prevail continuously 

 throughout the lower part of the sandstone. At the 150 foot level, 

 tracks were traced laterally for a distance of 700 to 800 feet. 



The Coconino sandstone is described by Noble as follows: '' 



The Coconino sandstone is a pale-buff fine-grained cross-bedded sandstone 

 whose distinctive features are its massive appearance, the huge scale of the 

 cross-bedding, and the uniform fineness of the component grains of sand. The 

 massiveness of the sandstone, which is due to the coarseness of the cross- 

 bedding, causes it to weather into the highest and most precipitous cliff in the 

 upper wall of the canyon. 



The formation is made up of lenticular beds, each of which is truncated 

 by the bed above it in such a way that, as outlined in cross section or cliff 

 faces, the beds commonly form irregular wedges whose sides are sweeping 

 curvfes. Each wedge consists of innumerable thin inclined laminae. Horizontal 

 bedding is absent except near the base of the formation, where it is incon- 

 spicuous. . . . The laminae form parallel curves that flatten downward. 

 Commonly at the top of a wedge they are inclined at angles of 15° to 25°, or 

 exceptionally 30°, but near the base of a wedge they bend and become hori- 

 zontal or nearly horizontal. 



The fossil tracks occur on the upper surface of these inclined 

 laminae. In removing the laminae it was found that the underlying 

 surfaces were often devoid of tracks, while the very next layer might 

 be thickly covered. Sometimes as many as four distinct kinds of 

 tracks were found on one surface. Some slabs were literally covered 

 with imprints and curiously enough all pointed in the same direc- 



^ Noble, L. F., Prof. Paper 131, U. S. Geol. Surv., 1922, p. 26, pi. 19. 

 ^ Op. cit., p. 66. 



