CORRELATIONS 681 



species of reptiles known from the same system of sediments. From this 

 it is seen that the Pennsylvanian fauna is a distinctly amphibian fauna, 

 91 per cent of its genera being unknown in rocks higher than the Neva 

 limestone ; 50 per cent of the Eeptiles go over into the beds higher than 

 the Neva limestone. 



In contrast with this condition we find in beds above the horizon of the 

 Neva limestone (none of the beds within about 100 feet of it are known 

 to contain air-breathing vertebrate remains) a very different relation of 

 the two classes of animals. Thus there are only 22 genera and 39 species 

 of Amphibia in these higher beds, while there is a total of 35 genera and 

 57 species of reptiles, which constitute a distinctly reptilian fauna in con- 

 tradistinction to the amphibian fauna of the Pennsylvanian. 



Taking the fauna in detail by formations, or stages, we find in the 

 Wichita beds and their equivalent in Oklahoma 11 genera and 15 species 

 of Amphibia, of which only four genera have come up from below, while 

 there are 18 genera and 36 species of reptiles known from this stage, only 

 three of the genera having persisted from the Pennsylvanian beds, leaving 

 15 out of the 18 genera introduced during the Wichita stage. 



In the Clear Fork beds there are 16 genera of Amphibia, represented 

 by 26 species — an increase in numbers over those known from the Wichita 

 stage, but still below the Pennsylvanian numbers. The Clear Fork Rep- 

 tilia are represented by 27 genera and 41 species, showing a marked and 

 consistent increase over those from the Wichita beds. 



This fact in itself is a very significant illustration of the faunal changes 

 brought about during earliest Permian time. However, if we take into 

 account the extensive specialization of many of the Permian reptiles, 

 such as Dimetrodon, Celpsydrops, and others, the case comes to have far 

 greater significance. To sum up the history of the air-breathing verte- 

 brates of the Pennsylvanian and Permian, we start with a pure Amphib- 

 ian fauna in the lower Allegheny, extending to the upper Allegheny, and 

 a mixed Amphibian-Reptilian fauna above this horizon, with the Am- 

 phibia in overwhelming preponderance to the base of the Permian, when 

 the Reptilian forms preponderate and are extremely specialized. 



From the data at hand it is apparent that, so far as our knowledge goes, 

 the air-breathing Vertebrata show very much the same history for the 

 periods of time under consideration as do the invertebrates and the plants. 



When measured in the terms of western sedimentary deposits, these 

 fossils are distributed through some 5,000 or more feet of deposits nearly 

 equally divided between the Pennsylvanian and Permian rocks, composed 

 of shales, limestones, sandstones, and coals. The fauna clearly shows two 

 distinct facies in the lower and upper part of these beds. 



XLV — Bull. Geol. Soc. Am., Vol. 33, 1921 



