48 



C. R. Longwell — Geology of 



observed was 75 feet, and the formation thins consistently 

 westward, losing its identity in the Muddy Eange. 



The Kaibah limestone has two thick limestone mem- 

 bers, both composed of dark gray, cherty limestone in 

 heavy beds. In Grand Wash these members are separ- 

 ated by red sandstone, but in the Virgin and Muddy 

 Mountains the dividing horizon is occupied by massive 

 gypsum which is locally 100 feet thick. At the base the 

 formation has alternating layers of sandstone and lime- 

 stone, forming a variable thickness. The total thickness 

 of the formation ranges from 400 to 700 feet. Fossils are 



Fig. 3. — Upper Grand Wash Cliff, 10 miles north from the mouth of the 

 Grand Canyon. Thickness of strata exposed about 900 feet. 1, upper 

 part of Supai sandstone; 2, Coconino sandstone; 3, alternating sandstone 

 and limestone layers at base of Kaibab limestone; 4, lower heavy lime- 

 stone member of the Kaibab; 5, upper heavy limestone member. Bench 

 between 4 and 5 due to weak shale and sandstone. 



abundant in the hea^^ limestone members. Dr. Girty has 

 identified the following list: Fiskdipora sp., Leptopora 

 n. sp., Phyllopora n. sp., Cystodicfya sp., Enteletesf n. sp., 

 Derhya sp., Productus ivesi, P. occidentalis, P. semiretic- 

 ulatus, Marginifera lasallensisf , Pustula subhorrida, P. 

 montpelierensis , Squamularia aff. guadalupensis, Com- 

 posita suhtilita, C. mexicana, Griffithides sp., and Acan- 

 thopecten coloradoensis. 



Dr. Girty states that this fauna is Permian, cor- 

 responding to that of the typical Kaibab and also to the 



