0. Schuchert — Russian Carboniferous and Permian. 151 



Regarding these formations and their correlation, Girtj 

 writes :- 



"The Carboniferous faunas of the Trans-Pecos region, espe- 

 cially the upper ones, differ widely from those of the Central 

 and Eastern States. The fauna of the Hueco formation, how- 

 ever, is found with some modifications over most of the area 

 west of the Rocky Mountains; but the remarkable group of 

 fossils occurring in the Capitan limestone is only known in the 

 Guadalupe Mountains. The fauna of the Capitan limestone 

 differs to a marked degree from that of the Hueco formation, 

 and was assigned to the Permian epoch both by Shumard, its 

 original discoverer, and by Girty. The fact that the faunas of 

 the Hueco formation in some respects strikingly resemble those 

 of the Spirifer marcoui zone, the Omphalotrochus whitneyi 

 zone, the Productus cora zone and the Schwagerina zone of 

 the Carboniferous section of eastern Russia, which immediately 

 underlie the typical Permian, seems to support the views of 

 these authors. On the other hand, there are some matters of 

 difference between the Russian faunas and those of the Hueco 

 formation, part of which are points of agreement with the Capi- 

 tan fauna. Thus, the Russian faunas, even the highest (that 

 of the Schwagerina zone), seem, aside from containing aspects 

 not found in either, to combine features of both the Hueconian 

 and the Capitan faunas, features, moreover, which these for- 

 mations do not possess in common. 



" The American beds can hardly be looked on as being a 

 mere expansion of the Russian series, since the Hueco, Dela- 

 ware Mountain and Capitan formations combined have a thick- 

 ness much exceeding 5000 feet, while the four zones recognized 

 by Tschernyschew are considerably less than 1000 feet thick. In 

 view, therefore, of the preponderating resemblance shown in 

 the Hueco faunas and the differences in that of the Capitan 

 limestone, the latter is retained under the title of Permian, 

 and with it, provisionally, the Delaware Mountain formation " 

 (2, pp. 42-43). 



The latest paper by this same author makes the following 

 important statement regarding the Permian question, and 

 gives his views concerning the equivalence of the formations 

 in the various American regions :— 



" The opinion has been expressed that the Pennsylvanian 

 faunas of eastern and western United States may belong in 

 different provinces, and that they are probably to some extent 

 equivalent. The belief is tentatively held that the highest of 

 our Western horizons are considerably younger than the high- 

 est known invertebrate horizons of the East, those of the Kan- 

 sas section, for instance, which are characteristic of the so-called 

 Permian of the Mississippi Valley. In spite of the able pen 



