66 



SHORTER CONTRIBUTIOJfS TO GENERAL GEOLOGY, 1921. 



TERTIARY (?) AND QUATERNARY ROCKS 



Basaltic flows, apparently of late ilate, in 



places little weathered and with only a thin 



soil cover, occupy considerable areas of the 



region. Associated with them arc local thick 



boulder beds and here and there cinder cones. 



(See Pis. XII; XIII, B.) At some places 



large areas of dune sand occur, notably that 8 



miles southeast of St. George. Along Virgin 



River alluvial flats supply land for irrigation 



farming. 



AGE OF THE FORMATIONS. 



The Rcdwall limestone at the locality of its 

 typical occurrence is believed to be in part 

 Mississippian and in part Penn.sylvanian. In 

 the Beaverdam Mountains we collected Mar- 

 ginifera afi". M. Kpleiidens (catalog No. 3059) 

 at a horizon 650 to 700 feet beneath the top of 

 the formation, and Chaftetcs! millfporaceus (cat- 

 alog No. 3061) at a horizon about 1,000 feet 

 beneath the top. G. II. Girty reports botli 

 these species to indicate either Pennsylvanian 

 or Permian age. It is therefore probable that 

 at least 1,000 feet of the Iledwall limestone, as 

 here conceived, is Pennsylvanian. 



The Supai formation, Coconino sandstone, 

 and Kaibab limestone for years were consid- 

 ered to represent the Pennsylvanian. The 

 evidence accumulated from many sources, 

 however, is increasingly in favor of a correla- 

 tion of all three formations with the Manzano 

 group of New Mexico, now classilied as Per- 

 mian. In this paper the Supai formation and 

 the Coconino santlstone are assigned doul)t- 

 fully to the Pennsylvanian and the Permian, 

 respectively, as the available evidence of their 

 age is still insufficient to warrant a definite 

 assigrmient. The Kaibab limestone is placed 

 in the Permian, because it afforded a number 

 of lots of fossils, and although no attempt was 

 made to gather complete collections, those 

 obtained permit correlation with part of the 

 Manzano group. The following combined lists 

 .show the determinations made by Mr. Girty: 



1. Five collections (catalog Noa. 3054 to 3()5S) from the 

 •' Bellerophon limestone" of the Harriaburg gypsiferous 

 member: 



Phyllopora? sp. 



Dielasma sp. 



Nucula jevatiformis. 



Lefla ol>esa. 



Pteria (liakewellia'?) sp. 



Pseuilomonotis? sp. 



Myalina sp. 



SchizocUis wheeleri. 

 Aviculipecten? sp. 

 Pleurophorus mexicanus. 

 Plagioglypta caniia. 

 Bellerophon majusculus. 

 Hucanopsis aff. B. bella. 

 iMiphemus sp. 

 Pleurotomaria sp. 

 (loniospira sp. 

 Naticopsis? sp. 

 Platyceras sp. 

 Eumophalus sp. 

 Metacoceras sp. 

 Nautilus sp. 



2. Vi\f collections (catalog Nos. 3047 to 3051 ) from lowei 

 strata of the Harrisburg gypsiferous member; 



Batostomella n. sp. 

 Poiypora sp. 

 Phyllopora? sp. 

 Derbya? sp. 

 ( 'honetes hillanus. 

 Pugnax osagensis var. 

 Spirifer sp. 

 Spirit erina sp. 

 Squamularia guadalupensis. 

 Composita subtilita. 

 Composita n. sp. 

 Myalina aff. M. deltoidea. 



3. A single lot (catalog No. 30(j0l from a coral-ljearing 

 limestone near the top of the Harrisljurg gypsiferous mem- 

 ber in the Harri.slmrg dome: 



Favosites':' n. sp. 

 Lithostrotion? n. sp. 

 Campophyllum? n. sp. 



4. Eight collections (catalog Nos. 3039 to .3046) from the 

 massive limestone members of the Kaibab limestone; 



Sponge, undetermined. 

 F.chinocrinus sp. 

 Spirorbis sp. 

 Batosomella n. sp. 

 Lioclema sp. 

 Fenestella sp. 

 Poiypora sp. 

 Septopora n. sp. 

 Derbya aff. D. nasuta. 

 Orthotetes sp. 

 Meekella pyramidalis. 

 Chonetes hillanus. 

 Productus ivesi. 

 Productus occidentalis. 

 Productus popei. 

 Pustula subhorrida. 

 Pustula subhorrida var. 

 Pustula aff. P. irginae. 

 Marginifera splendens? 

 Marginifera'.' aff. M. splendens. 

 Dielasma sp. 



Squanndaria guadalupensis. 

 Spiriferina sp, 

 Composita mexicana? 

 Composita subtilita. 

 Pseudomonotis'.' sp. 



