CHAPTER XXI 



THE PERMIAN PERIOD 



FORMATIONS AND PHYSICAL HISTORY 



At the close of the Pennsylvanian period much of the central 

 and eastern parts of the United States became dry land, and the 

 sea-covered area in the west was greatly restricted. The area of 

 land was perhaps as large as at any time since the beginning of the 

 Paleozoic. The waters which still lay upon the continent were 

 partly in the form of lakes and inland seas, and partly connected 

 with the open ocean; but the areas which the sea overspread at the 

 beginning of the period were largely abandoned before its close. 

 These changes in geography reflected themselves both in the distri- 

 bution of the Permian formations and in their character. 



East of the Mississippi. During the earlier part of the period 

 fresh-water sedimentation continued much as before in some parts 

 of the east (parts of Pennsylvania, West Virginia, Maryland, and 

 Ohio), and with the commoner sorts of sedimentary rocks there is 

 some coal. There, and in and about Nova Scotia, non-marine 

 Permian strata rest on Pennsylvanian beds in such a way as to show 

 that sedimentation was not seriously interrupted. The systems are 

 separated on the basis of fossils. Recently, a conglomerate forma- 

 tion (the Roxbury) of Eastern Massachusetts has been interpreted as 

 of glacial origin. This origin suggests its reference to the Permian 1 . 



West of the Mississippi. West of the Mississippi the system is 

 better developed, being partly marine and partly non-marine. In 

 Kansas and Nebraska its lower part is marine, and the Permian 

 of these states is probably continued northwestward to Wyoming 

 and South Dakota. The marine Permian of Kansas is overlain by 

 beds containing gypsum and salt, and possessing other features 

 which show that the open sea of the region was succeeded by dis- 

 severed remnants, or by salt lakes whose supply of fresh water was 

 exceeded by evaporation. With the saline and gypsiferous deposits, 

 and above them, are the "Red Beds," many of which are Permian. 



1 Sayles, Bull. Mus. Comp. Zool. Vol. LVI. (Geol. Ser. X) pp. 141-170, and 

 Science, Vol. 32 (1910) p. 723. 



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