THE PERMIAN PERIOD. 625 



the longitude of Texas and Kansas, are often highly colored, red being 

 the dominant hue. This color so often characterizes formations known 

 to have been made in inclosed basins, that the connection can hardly 

 be fortuitous. 



It is a singular fact, though it may be no more than a coincidence, 

 that certain thin but well-defined layers of clay in the Permian beds 

 of Texas, like certain layers of the Permian in Europe, contain con- 

 siderable quantities of copper ore. In Europe, however, the copper 

 is confined to a single layer, while in Texas it is distributed through 

 several. This correspondence is perhaps worthy of mention, especially 

 because copper ores are not, on the whole, abundantly distributed, 

 and this is not their usual mode of occurrence. 



Thickness. — In the Appalachian region, the Lower Permian beds, 

 sandstone and shale, with thin seams of coal, have a thickness of about 

 1000 feet. The Upper Permian is wanting. In Kansas the thickness 

 is twice as great, while in Texas it reaches 7000 feet. The Permian 

 system, like the Carboniferous, is thicker in the southern interior than 

 in the Appalachian region. 



Correlation. — In the region east of the Mississippi, the Permian 

 is so closely associated with the Coal Measures that the two were for- 

 merly classed together. Were this region only considered, this would 

 appear to be the best classification. In the western part of the con- 

 tinent, on the other hand, the differentiation of the Permian from 

 the Carboniferous is more distinct, and its relation with the Trias is 

 generally close. In the Texas-Kansan region, for example, the rela- 

 tions of the Permian to the Trias, if the beds referred to the Trias 

 are really such, are so close as to have caused the frequent reference of 

 the upper part of the former to the latter. Perhaps the Permian 

 period is best looked upon as a transition period from the Carbon- 

 iferous to the Trias, and so from the Paleozoic to the Mesozoic. Accord- 

 ing to this view, its close relationship to the underlying system in 

 some places, and to the overlying system in others, is natural. 



The Foreign Permian. 



Europe. 



In Europe, as in America, the Carboniferous period was brought 

 to a close by very considerable changes, for much of the area which 



