142 ENVIRONMENT OF VERTEBRATE LIFE, ETC. 



which attains prominence in some places. This sandstone, together with the 

 overlying gypsum, apparently constitutes Herrick's 'Permian.' In the classi- 

 fication here adopted the upper limit of the Abo formation is drawn below the 

 gypsum for the ob-vious reason that in many places the overlying or Yeso forma- 

 tion contains beds of gypsum and gypsiferous shale at several horizons, through 

 a thickness in some places of i ,000 feet or more. 



" Yeso formation. — The Yeso formation * * * lies with apparent conformity 

 upon the Abo sandstone, and consists of 1,000 to 2,000 feet of sandstone, shale, 

 earthy limestone, and gypsum. The sandstone varies in color from gray to 

 many shades of pink, yellow, red, and purple, and in texture from soft, coarse- 

 grained, friable masses to fine-grained layers, evenly bedded and flinty. The 

 shales, frequently gypsiferous, are soft, pink to yellow in color, and beds of massive 

 white gypsum 100 to 200 feet thick occur in many places. 



''San Andreas limestone. — * * * It consists essentially of massive limestone, 

 which is often cherty and poorly fossiliferous, although several localities were 

 found where fossils are abundant. * * *" 



The discovery by Case of Permian vertebrates in the Abo sandstone 

 northeast of Socorro, New Mexico,^ similar to or identical with those occur- 

 ring in the EI Cobre Canyon and in the Arroya de Agua, Rio Arriba County, 

 New Mexico, shows that these deposits belong In the Basin Province. 



Whether It will later be proven that the Abo Is continuous with the 

 red sandstone of the Pecos Valley around the southern side of the Guadalupe 

 range Is uncertain, but there can be little doubt that the beds occupy an 

 equivalent or somewhat lower position. Wllllston- and Wllllston and Case^ 

 have asserted their belief based on the stage of development of the forms, 

 found, that the beds of Rio Arriba County, are younger than those of Texas, 

 and later Wllllston^ expressed his belief that the El Cobre beds of New Mexico 

 are the equivalent of the Wichita beds of Texas. Beyond this there Is no 

 evidence of their relative position. 



Lee and Glrty^ believe that these beds are the equivalent of the Texas 

 beds. They say that an uplift occurred In the Rio Grande Valley Imme- 

 diately preceding the deposition of the Manzano beds; then the red beds 

 of the lower part of the Manzano group were deposited, which are equivalent 

 to the red beds of eastern Colorado and to the red beds of Texas. 



To the southwest the lower part of the Manzano group Is apparently 

 lacking. Darton has described the Gym limestone which he regards as 

 the upper part of the Manzano, In two papers. In 1916 he said:** 



' Case, E. C, Further Evidence Bearing on the Age of the Red Beds in the Rio Grande 

 Valley, New Mexico, Science, vol. 44, pp. 708-709, 1916. 



^ Williston, S. W., The Permo-Carboniferous of Northern New Mexico, Jour. Geol., vol. 

 XX, pp. 1-12, 1912. 



' Williston, S. W., and E. C. Case, Permo-Carboniferous Vertebrates from New Mexico, 

 Carnegie Inst. Wash. Pub. No. 181, 1913. 



* Williston, in C. R. Stauffer, Divisions and Correlations of the Dunkard Series of Ohio, 

 Bull. Geol. Soc. Amer., vol. 27, p. 88, 1915. 



'' Lee, W. T., and G. H. Girty, The Manzano Group of the Rio Grande Valley, U. S. Geo- 

 logical Survey Bull. 389, 1909. 



' Darton, N. H., Geology and Underground Waters of Luna County, New Mexico, U. S. 

 Geological Survey Bull. 618, 1916. 



