the Muddy Mountains, Nevada, etc. 47 



ing fossils : Triplopliyllum sp., Productus cora, Pustula 

 nebraskensis, P. nehraskensis var., Dielasma hovidens, 

 Spirifer cameratus, 8. rockymontanus, S. sp., Composita 

 suhtilita, Edmondia sp. On the basis of this fauna Dr. 

 Girty correlates the limestone with the Magdalena group 

 of New Mexico. In this paper the formation will be 

 called the Callville limestone, because of its prominence 

 in Callville Mountain. An indeterminate thickness has 

 been eroded from the sections studied in the Muddy 

 Mountains, and the contact with the overlying Supai sand- 

 stone was not seen at any place. Limestone with similar 

 fossils and lithology was recognized in the Virgin range. 

 In the Grand Wash Cliffs, limestone containing Pennsyl- 

 vanian fossils lies immediately beneath the typical Supai 

 sandstone, but the limestone does not resemble the Call- 

 ville formation lithologically. The thick series of strata 

 in the lower cliff contains an abundance of dolomite, and 

 does not resemble any part of the Callville Mountain Car- 

 boniferous section. 



The lower part of the Supai sandstone may be of Penn- 

 sylvanian age but for convenience the entire formation 

 will be discussed under the Permian. 



Permian System, — The Supai sandstone is prominently 

 exposed in the upper Grand Wash Cliff, and in tilted fault 

 blocks to the west. In the upper cliff the sandstone is 

 more than 1,000 feet thick, and practically all of it is 

 bright red, fine-grained, and regularly bedded. In the 

 Virgin and Muddy mountains cross-bedding is very prom- 

 inent in the formation, gypsum and gypsiferous shale 

 occur at several horizons, and in the most westerly ex- 

 posures the typical red color is largely replaced by grey. 

 No fossils were found in the sandstone, but at least a part 

 of it is assumed to be Permian, corresponding to the 

 Upper Supai described by Schuchert in the Grand 

 Canyon district. In the lower Grand Wash Cliff, Pennsyl- 

 vanian fossils were found near the top of beds which ap- 

 parently correspond to Noble's basal Supai in the Grand 

 Canyon. These beds may mark the upper limit of the 

 Pennsylvani'an, or the Pennsylvanian-Permian contact 

 may lie at a higher horizon, within the typical red sand- 

 stone. 



Typical Coconino sandstone lies above the Supai in 

 the Upper Cliff, in Grand Wash Valley, and in the Virgin 

 Mountains. In these exposures the maximum thickness 



