NO. 3 



GRAND CANYON FOSSIL FOOTPRINTS — GILMORE 



Kaibab , 

 limestone > 



Supai sandstone from 30 to 40 feet above the Hermit-Supai contact. 

 In the Supai, two levels some 25 or 30 feet apart near the middle 

 of that formation are track-bearing. Thus these evidences of past 

 life range through over 800 feet of 

 strata. These horizons lie, roughly 

 stated, as follows : Coconino, 900 to 

 1,030 feet ; Hermit, 1,350 to 1,400 feet ; 

 and Supai, i ,760 to i ,800 feet below the 

 top of the Canyon wall. 



At the present time tracks are known 

 in these formations on the Yaki and 

 Hermit Trails only, but doubtless their 

 geographical range will be rapidly ex- 

 tended now that their precise levels 

 have been ascertained. A more de- 

 tailed discussion of the occurrence and 

 character of the beds in which the 

 tracks are found is given below. 



Coconino sandstone. — The Coconino 

 sandstone and the manner of occur- 

 rence of its fossil footprints was dis- 

 cussed at some length in my previous 

 paper,^ and at this time it seems only 

 necessary to record such observations 

 as resulted from my later visit to the 

 Canyon. 



The curious fact that the trend of 

 nearly all of the tracks and trails was 

 in one direction, that is, up the slope 

 of the crossbedded sandstones, has pre- 

 viously been noted, and examination of 

 many additional hundred square feet 

 of track-covered surface of the Coco- 

 nino verifies this original observation. 

 In all of the hundreds of trails seen, 

 only three exceptions were found. It 

 should also be mentioned that where 

 tracks were seen in situ on the Yaki Trail, this same condition obtained. 



The vertical range of tracks in the Coconino seems to be confined 

 to the basal 150 feet of the formation of which the lowermost 20 

 are barren, and this same condition was found to prevail in the newly 



Fig. I. — Upper part of the 

 geological section on Hermit 

 Trail. Position and extent of 

 track-bearing strata indicated. 

 (Section (modified) after 

 Noble.) 



* Smithsonian Misc. Coll., Vol. 77, No. 9, 1926, pp. 1-41, pis. 1-12. 



