

uUu 



CHAPTER XIX 



THE CARBONIFEROUS PERIODS 



The Carboniferous formerly included the Lower Carboniferous 

 (Mississippian), the Upper Carboniferous (Pennsylvanian), and the 

 Permian. 1 American geologists have been led to the conclusion 

 that each of these three subdivisions is of a rank equal to that of the 

 Ordovician, Silurian, or Devonian, and should be called a period. In 

 this study it seems advisable to discuss the life of the three periods 

 together (the Lower and Upper Carboniferous, and Permian) since 

 by so doing the sequence of life changes can best be followed. 



Mississippian or Lower Carboniferous 



The epicontinental seas (Fig. 446) of the early portion of this period 

 were about as extensive as in the Devonian and occupied much the 

 same regions. As a result, over large areas the transition between 

 the Devonian and Mississippian is not indicated by abrupt changes. 

 Towards the close of the period (Fig. 447), the seas again became 

 constricted. 



The sediments brought into the Appalachian trough from the con- 

 tinent of Appalachia were for the most part coarse sands and muds. 

 Sun cracks, ripple marks, the footprints of amphibians, and other 

 evidences indicate an arid or semi-arid climate, and that the sediments 

 (Pocono and Mauch Chunk) 2 were portions of a great delta or alluvial 

 plain built by shifting streams which flowed over it. The Mississip- 

 pian conglomerates are important mountain makers in the Appala- 

 chians. 



In the central and western states the Mississippian sediments are 



1 The term Carboniferous was given because of the large quantities of coal (carbon) in the rocks 

 of the period. The subdivisions — Mississippian and Pennsylvanian — were named because 

 of the great development of the rocks of the periods in the Mississippi Valley and in Pennsyl- 

 vania respectively. The term Permian was given because of the wide extent in the province of 

 Perm in Russia. 



2 Barrell, J., — Origin and Significance of the Mauch Chunk Shale, Bull. Geol. Surv., Vol. 

 18, 1907, pp. 449-476. 



469 



