Schuchert — Carboniferous of Grand Canyon of Arizona. 357 



Lower Supai.— The Lower Supai formation begins 

 with a thick-bedded and cross-bedded cliff-making sand- 

 stone of about 150 feet in thickness. Beneath it are red 

 sandy shales with two bands of sandstones that together 

 have an estimated thickness of 200 feet. At the base of 

 this zone is another horizon of thin flaggy beds with 

 some sun-crack fillings and an abundance of rain-prints 

 of the mammillary kind, interpreted as having been made 

 by long-continued rain. Midribs of either ferns or cyca- 

 dofilices were seen, and probably also indistinct feet im- 

 prints of amphibians. The trail runs along this zone 

 for about 2 miles, and one has a fine opportunity to 

 study the sediments and to note the abundance of rain- 

 prints and a few rill-markings. 



The next lower zone is a cliff-making sandstone about 

 50 feet in height. Then follows one of shales 100 feet 

 thick, that near the top has beds of septaria-like limy 

 concretions embedded in a dark purple sandy mud. No 

 fossils were seen in them, and they give the impression 

 of being caliche formations. Associated are also thin 

 zones of intraformational conglomerates with flat and 

 somewhat rounded small pebbles ; the shale pieces have 

 blackened surfaces. 



Then follow the lower thick-bedded cliff -making Supai 

 sandstones, again cross-bedded and, like the upper ones, 

 about 150 feet in thickness. The top of this zone occurs 

 at the sign post "Bed Zigzags" and the whole is of a 

 pink color. 



The lowest zone of the Supai is about 250 feet in thick- 

 ness and consists in the main of shales interbedded with 

 many bands of sandstones. "Four Mile Camp" or 

 ' ' Point Lookout ' ' is near the center of this zone and here- 

 abouts occur pinkish arenaceous limestones with hori- 

 zons of red cherts that may be of diagenetic origin rather 

 than the result of weathering. Near the base of the 

 Supai are again seen thin-bedded flaggy sandstones 

 marked with rain-pittings and the fillings of sun-cracks ; 

 also the septaria-like limy concretions, up to 8 inches 

 across, interbedded with thin zones of oolites. No fossils 

 of any kind were seen. "Breezy Point" is near the base 

 of the Supai formation. 



In the field the writer got the impression that most or 

 all of the Supai as developed along the Hermit trail is of 

 fresh-water origin on a delta flood-plain of a river or 

 rivers fronting the sea. The basal beds with the oolites 



