CHAPTER XI 

 THE PENNSYLVANIAN (UPPER CARBONIFEROUS) PERIOD 



Origin of Name, Subdivisions, etc. 



As stated in the preceding chapter, the Pennsylvanian system 

 represents a part of what was formerly known as the Carboniferous 

 system in America. In other continents, strata equivalent to the 

 Pennsylvanian are usually called Upper Carboniferous. Rocks of 

 Pennsylvanian age include the Coal Measures proper of the old 

 Carboniferous, and they contain a far greater supply of workable 

 coal than the rocks of any other system. The name has been given 

 because of the typical development of the system with its coal in 

 Pennsylvania where it shows the following subdivisions generally 

 recognized in the eastern United States : 



Monongahela series (Upper Productive Coal Measures) 

 (Shales, sandstones, and limestones with much coal). 



Conemaugh series (Lower Barren Coal Measures) 



(Sandstones, conglomerates, shales, and limestones 

 with some coal). 

 insiLVAfliAJN ^ 2 Allegheny series (Lower Productive Coal Measures) 

 (Sandstones, shales, and limestones with much coal 

 and iron ore). 

 1. Pottsville series 



(Sandstones and conglomerates with some clays, lime- 

 stones, and coal). 



In the interior of the United States these four subdivisions 

 have scarcely been recognized as such. For example, in Iowa the 

 whole system is divided into two series: (1) Des Moines and (2) 

 Missourian. Local names are often employed in other portions of 

 the Mississippi Basin. In the western United States little has 

 been done toward subdividing the system. 



Distribution and Character of the Rocks 



General Distribution. — Only in the eastern part of the con- 

 tinent have the Mississippian and Pennsylvanian rocks been 



158 



Pennsylvanian 



