Schuchert — Carboniferous of Grand Canyon of Arizona. 353 



the time equivalent of more or less of the Moenkopi, Kai- 

 bab, and Coconino formations. 



SlJPAI FOEMATION. 



Beneath the Coconino formation lies the terraced and 

 slope-making Supai formation that is 1190 feet in thick- 

 ness. To the southward the formation has thinned to 

 600 feet in the Aubrey Cliffs. It is the most accessible 

 formation of all along the Hermit trail, and for nearly 

 4 miles in September, 1915, the newly made way had 

 thrown out the strata from the walls of the canyon. It 

 was therefore a most excellent time to study the deposits, 

 and, furthermore, Doctor Noble told me that there is no 

 equally accessible exposure of the Supai beds in all of the 

 Grand Canyon country. 



The Supai formation consists of alternating beds of 

 hard sandstones and soft shales, all of which are slightly 

 micaceous. The top 200 feet are sandy soft red shales. 

 The cross-bedded sandstones make cliffs and the shales 

 make slopes and ledges. The general color of the forma- 

 tion is a dull brick-red, but as a rule the sandy shales on 

 fresh fracture are bright red or maroon in color, while 

 the sandstones may be red or whitish, but as a rule are of 

 a dirty light greenish color. 



Upper Supai. — The rock character of the Supai forma- 

 tion is so variable from top to bottom that it is thought 

 best to describe the sequence in more detail as seen on 

 the Hermit trail. It will be described as the Upper and 

 Lower Supai; the former is 290 and the latter 900 feet 

 thick. Beginning at the top the contact with the Coco- 

 nino sandstone has been described. Beneath this plane 

 the Upper Supai consists of soft sandy red shales 

 through a thickness of about 200 feet (see fig. 2). In the 

 lower half are introduced thin beds of sandstone, and in 

 the next 90 feet the sandstones increase in thickness and 

 in number more and more. The base of this upper zone 

 occurs at the sign post "Red Top." 



Just below the sign "Red Top" in the lower turn of 

 the trail and immediately above the thick upper sand- 

 stone of the Lower Supai are seen thin-bedded red shaly 

 sandstones alternating with deep red zones of shale (see 

 fig. 3). The surfaces of the glistening and smooth platy 

 sandstones are replete with the fillings of the smail 



Am. Jour. Sci.— Fourth Series, Vol. XLV, No. 269.— May, 1918. 

 25 



