352 Sc/iuc/ierl — Carboniferous of Grand Canyon of Arizona. 



look Like at a distance of some hundreds of feet. They 

 arc also to be seen in several places on the Hermit trail 

 and here they are filled with undoubted Coconino sands. 

 The contact between the Supai and Coconino formations 

 is everywhere a sharp one, and the plane appears to lie 

 as level as such a surface can be. It is also an easily 

 recognizable disconformity. Above this plane is the 

 great cliff of yellowish white sands and beneath them 

 are the slopes of deep red or even maroon fine sandy 

 shales of the Supai. To the eye, no greater contrast in 

 sedimentation is possible than that on either side of this 

 disconformity, and the significance of this plane in His- 

 torical Geology will be discussed after a description of 

 the Supai formation and its fossils. However, as Doctor 

 Noble has seen so much more of this contact, it will be 

 best to restate what he has written in a letter of May 

 10, 1916 : 



"The fissures in the terminal Supai beds that are filled with 

 Coconino sand are certainly significant, but they may be a local 

 feature of the Coconino-Supai contact. I have examined this 

 contact on all the other trails and never found fissures. I 

 believe the contact between the Supai and Coconino, sharp 

 though it appears, is not so significant as the rough, ragged sur- 

 face of erosion within the Supai on the Hermit trail. I am 

 theref ore not sure that it is significant of a great time break. ' ' 



The question as to which one is the more significant 

 break will be discussed later. 



In this connection, it may not be out of place to direct 

 attention to evidence of arid climates in Permian time 

 throughout the Colorado Plateau country. To the east 

 of El Tovar, in the Navajo country, is the De Chelly fine- 

 grained sandstone, which in thickness varies from less 

 than 200 up to 800 feet. It is well described by Gregory, 5 

 from whom these data are taken. It is one of the most 

 cross-bedded formations known to geologists, and the 

 heterogeneity of the sweeping concave lines of sedimenta- 

 tion indicates that the De Chelly is a dune deposit of an 

 arid climate and of "a region of low relief bordering the 

 sea." It may well be that the marine Kaibab limestone 

 and the Coconino sandstone toward the east change 

 finally into desert dune deposits and that the De Chelly is 



5 H. E. Gregory, U. S. Geo! Purvey, Prof. Paper 93, pp. 31-34, 1917. 



