356 Schuchert — Carboniferous of Grand Canyon of Arizona. 



it is 550 feet," whereas the underlying sandstone phase 

 of the Lower Supai thins slightly in the same direction, 

 for on the Hermit trail the thickness is 900 feet and in 

 the northwestern part of the Shinumo quadrangle it is 

 850 feet. 



These facts show that there is probably an important 

 break in sedimentation in the upper portion of the Supai 

 formation, and that the Upper Supai has fossil plants 

 that seem to indicate a Permian age for these strata. 

 The Lower Supai along the Hermit trail has not yet fur- 

 nished any fossils, but to the northwest some 30 miles or 

 more the equivalent beds are more calcareous, and here 



Fig. 3. 



flipper Supai B>of Shale j| 



<?t Ctiffi Waring 

 Sayidshne • oT-Zower Supai 



Fig. 3. Diagram to illustrate erosional contact between Upper and Lower 

 Supai on Hermit trail. The fossils are from the beds on the lower turn of the 

 trail. After L. F. Noble (unpublished MS. of the U. S. Geological Survey). 



Pennsylvanian fossils have been secured. This will be 

 explained further on. This line of erosion in the Upper 

 Supai may therefore separate the Pennsylvanian from 

 the Permian. Furthermore, there is another break or 

 disconf ormity between the Upper Supai and the Coconino 

 formations, and it lies in early Permian deposits. Which 

 of the two breaks is the more important can not be 

 answered from a study of the limited area about El 

 Tovar, though to Doctor Noble, who has seen more of 

 the Grand Canyon than any other geologist, the lower 

 one is held to be of greater significance as a time break. 

 In any event, the disconformity between the Upper and 

 Lower Supai formations is of considerable importance 

 in American stratigraphy and seemingly points the way 

 for a satisfactory distinguishing between the records of 

 Pennsylvanian and Permian time in the Cordilleran area. 



