568 C. SCHUCHERT PALEOGEOGRAPHY OF XORTH AMERICA 



toidea and best agree with those of the Cuseler. He states that the 

 Palgeodictyoptera so characteristic of the Missourian are absent here. The 

 evidence furnished by the insects is therefore in harmony with that of the 

 plants. 



Permic of the Mississippian sea. — In this province the Missourian ma- 

 rine deposits pass without break into the "Permo-Carboniferous," and 

 stratigraphers have differed as to where in this section the line should be- 

 drawn between the Pennsylvanic and the Permic. There is no natural 

 limit here, and the line of separation must always be an arbitrary one. 

 The other debated question is, Shall these higher deposits be referred to 

 the Pennsylvanic or to the Permic system? The answer will depend on 

 whether the Permic shall be restricted to the type area — the Perm region 

 of the Ural mountains of Eussia — or whether the view shall be adopted 

 that the Eussian formation known as the Artinsk is best referred to the 

 Permic, using this term in the wider sense. The latter view is the one 

 more generally accepted, and also the one adopted here. Following the- 

 work of Prosser, the writer will therefore draw the Permic line at the 

 base of the AVreford limestone of Kansas. Not many typical Missourian 

 species pass above this line, and most of these begin in the upper part of 

 the Pennsylvanic. Of the 164 Kansas species listed by Girty, 198 46 pass 

 into the basal Permic beds known as the Chase and Sumner, and 12 are 

 restricted to them. Of the former, 24 range throughout the Missourian, 

 and some of these even from the Pottsvillian ; 14 others begin near the 

 middle of the Missourian, and 8 take their rise a little below the "Wref ord. 

 These figures show that there is here a complete transition, but, as will be 

 seen, the faunal changes are largely brought about by the dropping out of 

 the brachiopods and the appearance of new forms, chiefly pelecypods, but 

 in the south of ammonites. For this transition series the writer adopts 

 Keyes's Oklahomian, as his emended definition embraces all the so-called 

 Permo-Carboniferous. The series, therefore, represents the lower portion 

 of the Permic in the wider sense, and it is all probably older than the true 

 Permic of the Perm district of European Eussia. 



The more characteristic fossils of these transition beds are: Pseudo- 

 monotis hawni (this form also occurs below, and the genus goes about 

 half way down in the Missourian), Myalina aviculoides (below), M. per- 

 miana,Bakewellia ( ?) parva, (below) ,Pleuropliorus calhouni, P. sabcunea- 

 tus, Sedgwickia dltirostrata, Chcenomya leavenworthensis, C. minnehalia, 

 and Phacoceras dumblei (Fort Eiley limestone). Other forms not so 

 characteristic are : Orthotetes robu&ta, Meekella striaticostata, Productus- 

 nebrascensis, Marginifera wabasliensis, and Composita subtilita. 



188 Girty : Bull. no. 211, U. S. Geological Survey, 1903. 



