G. B. Richardson — Paleozoic Formations. 483 



rent and the rock is characteristically massive. Chemically 

 it is of variable composition, some analyses showing the pres- 

 ence of considerable magnesium while others indicate its 

 almost complete absence. Besides its main occurrence in the 

 Guadalupe Mountains the Capitan limestone was determined 

 in 1907 to be present in the southern end of the Delaware 

 Mountains, where it has been faulted down and adjoins the 

 limestone of the Delaware Mountain formation. P. S. Tarr 

 reports, in the paper cited above, the presence of 1000 feet or 

 more of sandstone lying above the Capitan. formation, but 

 these rocks have not been studied, so that neither the base nor 

 the top of the strata bearing the Guadalupian fauna has yet 

 been determined. It is expected that these relations can be 

 determined in the northward continuation of the formations in 

 the Sacramento Mountains of New Mexico. The following 

 is a short list of fossils typical of the Capitan limestone deter- 

 mined by Dr. Girty : 



List of fossils from the Capitan limestone. 



Fasulina elongata Squamidaria Guadalupensis 



Orthote'es Guadalupensis Spiriferina pyramidalis 



Chonetes Hillanus Composita emargincda 



Productus latidorsatus Pugnax Swallowiana 



Productus pinniformis Dielasma spatidatum 



Richthofenia Permiana Heterelasma Shumardianum 



Spirifer Mexicanus Leptodus Guadalupensis 



Resume. 



In both the El Paso and Yan Horn quadrangles the basal 

 Paleozoic strata are sandstones which lie unconformably on 

 pre-Cambrian rocks. These conditions are in accord with 

 observations elsewhere in southwestern United States, where 

 part of late Cambrian time was characterized by the deposition 

 of coarse arenaceous sediments in a sea which was advancing 

 on an old land surface. The succeeding record is of subsi- 

 dence, interrupted by probable emergences, and of the accumu- 

 tation in Ordovician, Silurian, and Upper Carboniferous time 

 of a great mass of limestone exceeding 5000 feet in thickness. 

 The presence in this limestone of fivedistinct faunas representing 

 the Beekmantown, Galena, Richmond, Niagara, and Peun- 

 sylvanian stages, and the absence of the intervening faunas 

 which are present in the complete Paleozoic section, imply a 

 number of unconformities to account for the hiatuses, yet 

 these are not lithologically well marked and their exact strati- 

 graphic positions generally are unrecognizable. It is especially 

 noteworthy that in the Franklin Mountains Upper Carboniferous 



