476 HISTORICAL GEOLOGY 



Permian 



In North America the Permian is a continuation of the Pennsyl- 

 vanian and is a period in which the far-reaching seas of the latter were 

 withdrawn. Where the two systems occur in the same section in 

 North America they are almost always conformable. It is, however, 

 more important as the transition period between the Paleozoic and 

 the Mesozoic. In the eastern United States the comparatively small 

 areas of Permian rocks are separated from the underlying Pennsyl- 

 vanian on the basis of their plant remains, which are more closely re- 

 lated to European Permian plants than to those of the underlying 

 Pennsylvanian. They consist of about iooo feet of sandstone, shale, 

 and limestone, and a few beds of coal. 



In Nova Scotia, New Brunswick, and Prince Edward Island, strata 

 composed of red shale and sandstone are believed to have been 

 deposited in an inclosed basin during the Permian. 



During the early portion of the period a shallow sea extended from 

 the Gulf of Mexico through Texas into Kansas and Nebraska, as is 

 shown by the presence of marine fossils in the rocks. Later in the 

 period the sea withdrew, leaving a great region dotted here and there 

 with salt lakes which left beds of gypsum and salt, upon drying. The 

 aridity of the climate of this area is shown not only by the presence 

 of the salt and gypsum, but by the sun-cracked and ripple-marked red 

 sandstones and soft red shales or " red beds." It was a region not 

 unlike the Great Basin of Utah of to-day. These desert conditions 

 continued into the Triassic, and it is, consequently, difficult and in 

 many cases impossible to determine the dividing line between the 

 two systems. Portions of the Pacific border were covered with seas 

 in which marine life abounded. 



Before the close of the period the epicontinental seas had, with 

 one or two exceptions, withdrawn from the continent. 



Permian Glaciation. — One of the surprising features of the Permian 

 is the evidence of widespread glaciation during the period. The lo- 

 cation of the glaciated areas is also remarkable. They occur on both 

 sides of the equator and within 18 to 21 degrees of it; that is, they 

 extend slightly within the torrid zone. The limits of these ancient 

 glaciers are not definitely known, since the evidence has been largely 

 obliterated, but the proof at hand implies an area greater than that 

 during the " Great Ice Age." 



The proof of this ancient glaciation is conclusive and consists of 



