PERMIAN GROUP. 77 



cient to determine the age of the rocks, but some of the invertebrate characteristic 

 fossils of wide geographical distribution are : Fusulina cylindrica, Lophophyllum pro- 

 liferum, Spirifera camerata, Productus rogersi, P. nebraskemis, P. longispinus, Chone- 

 tes mesolobus, Athyris subtilita, Spiriferina kentuckiensis, Macrodon carbonarius, Allor- 

 isma subeuneatum, Aviculopecten rectilaterarius, Pernopecten aviculatus, Pinna peracuta, 

 Crenipecten retiferus, Myalina subquadrata, Bellerophon carbonarius, Pleurotomaria tab- 

 ulata, P. sph&rulata, MacrochUina gracilis, M. primigenia, M. kansasensis, M. cari- 

 nata, Nautilus mvssouriensis, PhUlipsia missouriensis, and P. sangamonensis. 



CHAPTER XXXIV. 



PERMIAN GROUF>. 



168. This Group was described by Murchison in 1845, in Russia and the 

 Ural Mountains, and named from Perm, in Russia. It was first ascertained in 

 this country by Swallow in 1858, in Kansas, where it has a thickness of 320 feet. 

 Norwood announced its existence in Illinois, and Shumard described it in the Guada- 

 lupe Mountains of New Mexico, where it consists of white limestone, having a 

 thickness of 1,000 feet. In Kansas it consists of magnesian limestone, marls, 

 shales, conglomerates, and gypsum ; the magnesian character increases southerly to 

 New Mexico. Fossils are abundant on the Cotton wood, with sun-cracks and ripple 

 marks, and sometimes small piles of fossils and fragments appear, as if washed together. 

 It is conformable with the Coal Measures. In Pennsylvania the Upper Barren Meas- 

 ures, having a thickness of 1,000 feet, are referred to it. It is claimed the reptilian re- 

 mains in Illinois and Texas have shown its existence in those States. It is always 

 unconformable with the rocks above, in this country and elsewhere. Characteristic 

 species are Pseudomonotis hawni, Myalina permiana, Bakevdlia parva, Monotis halli, and 

 Pleurophorus subcuneatus. 



169. This Group closes the Palaeozoic series, to which this work is chiefly de- 

 voted. All the Groups exist in New York and Pennsylvania, except the subdi- 

 visions of the Subcarboniferous can not be distinguished, and the doubtful Quebec 

 Group has no existence there. The maximum thickness in these States is about 

 38,000 feet. Some of the Groups in the Lower Silurian have greater thickness in 

 other States than they have in these two, and the Coal Measures are much thicker 

 in Nova Scotia than they are in Pennsylvania. The whole Palaeozoic series in the 

 western ranges of mountains has an estimated thickness of about 40,000 feet. 



