PEKXSYLVANIC-PERMIC PERIOD 559 



tioned. The correlations thus far made are based on stratigraphy, ratified 

 by the excellent floral knowledge of David White, which has been pub- 

 lished in a number of papers. The map of Upper Pottsville time is 

 chiefly founded on the evidence furnished by the flora and on certain 

 correlations made by Girty. He states: 173 



"The Pottsville group has a distinct fauna and appreciable changes occur in 

 the later Pennsylvanian. But the changes are by no means so marked as one 

 would be led to expect from the thickness of the strata involved, the extent of 

 the territory they cover, and the varying conditions of the time and the place." 



In the Appalachian region, Girty 174 states that 



"The Pottsville series is righly fossiliferous in the way of fossil plants, but fur- 

 nishes as a rule few invertebrates. The invertebrate faunas are, except in a 

 few instances, peculiar and restricted, and clearly indicate unusual environ- 

 mental conditions. The most frequent fossil is 'Naiadites elongatus Dawson, 

 with which are associated bivalve crustaceans, such as Estheria, Leaia, and 

 Ostracods [also Spirorbis] ; while more rarely fragments of Prestwichia, or 

 Limuloids, or fish scales and plates are brought to view. An occasional Pec- 

 tinoid, almost always of the type of Arviculopecten whitei, together, not infre- 

 quently, with Lingula and Oi'Mculoidea, indicates that these faunas cannot be 

 considered as owing their peculiar facies to strictly fresh-water conditions." 



In Arkansas the Pottsvillian series begins with the Morrow, which, 

 according to D. White, has a flora "of latest or earliest Upper Pottsville 

 age." In the upper part of the Morrow is the Kessler limestone, beneath 

 which is the shale with the Pottsville flora, followed by the Brentwood or 

 Pentremital limestone. The fauna is largely new, but some of the old 

 species are : Pentremites rusticus, Spiriferina transversa, Hustedia, and 

 Squamularia. "Few paleontologists will at first be willing to accept 

 Pentremites as ranging above the top of the sub- Carboniferous, but the 

 evidence at hand leaves no other conclusion tenable" (Girty, 1905, 9). 



In the far West occur other pentremite faunas usually regarded as of 

 late "Mississippic" age. These were collected by the Hayden survey and 

 listed by Meek. 175 One lot is from "Old Baldy," near Virginia City, 

 Montana, and among other forms includes Pentremites symmetricus, P. 

 godoni ?, Schizophoria resupinata, Composita subtil ita, Dielasma bovi- 

 dens ?, Astartella neivberryi ?, Trepospira spliwrulata, etcetera. In the 

 light of the Arkansas collections these fossils must now be referred to the 

 Pottsvillian. At another place on the "Divide between Eoss fork and 

 Lincoln valley, Montana," is found a different fauna, according to Meek 



173 Girty : Journal of Geology, vol. 17, 1909, p. 309. 



174 Girty : Proceedings of the Washington Academy of Sciences, vol. 7, 1905, p. 8. 



175 Meek : Sixth Annual Report of the IT. S. Geological Survey of the Territories for 

 1872, 1878. 



