CHAPTER XII 



THE PERMIAN PERIOD 



Origin of Name, Subdivisions, etc. 



This period was so named by Murchison in 1841 because of 

 the widespread development of rocks of this age in the Russian 

 province of Perm. It is pretty distinctly a transition period be- 

 tween the Paleozoic and Mesozoic eras. In both the eastern and 

 western United States the Pennsylvanian rocks usually grade 

 upward into the Permian, while in the western regions the Permian 

 strata nearly always grade upward into the Triassic. Thus it is 

 well-nigh impossible to sharply separate the Permian from the 

 systems immediately above and below it, and the delimitation of 

 the Permian system in western America is by no means a settled 

 matter at the present time. The scarcity or absence of fossils in 

 many of the western areas adds to the difficulty. 



The following table will give a general idea of the subdivisions 

 now recognized in some of the better known regions, though it must 

 be clearly understood that precise correlations are not meant to 

 be implied. 



Texas 



Kansas 



Permian 

 System 



Double Mountain series 



(Salt, gypsum, and 



limestone). 

 Clear Fork series 



(Limestone and red 



clay) . 

 Wichita series 



(Red clay, sandstone, 



and limestone). 



Cimarron (Red Beds) series 

 (Sandstones, shales, dolo- 

 mites, and gypsum). 



Big Blue series 



(Shales and limestones). 



Pennsylvania 



Dunkard 



series 

 (Sandstones, 

 shales, lime- 

 stones, and 

 some coal.) 



ISO 



