HOMOTAXIAL EQUIVALENTS OF THE PERMIAN 335 



The chronologic equivalence and comparison of rocks being 

 universally based almost wholly upon the standard of the fossils 

 is at best a very uncertain criterion. In the case of the Permian 

 this uncertainty has been increased tenfold on account of the 

 peculiar treatment that the fossils have received. The investiga- 

 tion of the biotic characteristics of the Upper Paleozoic has been 

 very unsymmetrically developed and very unequally carried out. 

 This is true in both Russia and America. From the published 

 material no comparison of faunas is really possible ; that is, in 

 the sense that modern work demands. This chaotic condition 

 of affairs is not anomalous. It occurs with many other faunas 

 from many different horizons. In the present instance it is 

 merely accentuated by a combination of accidental circumstances. 



A most noteworthy factor is the extreme local character of 

 the well known, published information. A single American 

 instance suffices for illustration. Our best knowledge of the 

 faunas of the Upper Coal Measures (Missourian) is derived almost 

 entirely from a single horizon, at the single locality of Platts- 

 mouth, Nebraska. This place has been made classic by Geinitz 

 and Meek. All faunal comparisons, made through secondary 

 means, of the rocks of the Mississippi valley above the lower 

 productive Coal Measures (Des Moines) can take into considera- 

 tion only the little pamphlet of Geinitz and the thin volume of 

 Meek. Much has been made of this horizon by Waagen, 

 Tschernyschew and other foreign paleontologists. Our American 

 workers among the fossils have also depended largely upon the 

 same sources of information. 



As a matter of fact, the fauna of the Plattsmouth is charac- 

 teristic not of a single, insignificant terrane, but of the entire 

 Missourian series, and upward almost to the limits of the fossil- 

 iferous zones of the upper Paleozoic of the region — that is to 

 the Marion. To be sure, as to numbers, the various species are 

 differently represented at the several horizons; some forms are 

 not reported yet from this level or that one ; others appear that 

 are not recorded from the Plattsmouth beds ; yet, for a region 

 in which no effort has ever been made to exploit systematically 



