THE PENNSYLVANIAN PERIOD. 549 



where the Pennsylvanian rests on formations older than the Mis- 

 sissippian. This is the case in Illinois, 1 Iowa, 2 Indian Territory, 3 

 and elsewhere. The absence of Mississippian formations in these 

 several situations may be due either to failure of deposition, or to 

 post-Mississippian-pre-Pennsyl vanian erosion . 



Figs. 242 and 243 illustrate further the constitution of the system 

 in the east, and Fig. 244 its structure at a point in the western part 

 of the Appalachian Mountain system. 



East of the Appalachians. — The Carboniferous system occurs in 

 the vicinity of Narragansett Bay, 4 where it has an aggregate thickness 

 of about 12,000 feet, and often rests on beds of Cambrian age. The 

 Mississippian system appears to be wanting in this region, thus afford- 

 ing another bit of evidence of the distinctness of the Pennsylvanian 

 and Mississippian periods. The Pennsylvanian system of this region 

 carries coal, which is, however, too highly anthracitic (or graphitic) 

 to burn readily. The beds are much deformed and locally highiv 

 metamorphosed. They are associated with igneous rocks, some of 

 which are pre-Carboniferous. 



Carboniferous rocks of undetermined extent occur at other points 

 in New England, 5 where they are partly igneous (Fig. 245) or-meta- 

 igneous, and partly meta-sedimentary. They are sometimes so com- 

 pletely metamorphic as to make the determination of their age and 

 relations difficult and uncertain. 



Northeast of New England, in Cape Breton, Nova Scotia, and New 

 Brunswick, the Pennsylvanian system is extensively developed. Its 

 general constitution, including rich beds of coal, is similar to that 

 of the corresponding system in the eastern part of the United States. 

 From the nature of the formations, the existence of conditions similar 

 to those in the eastern interior is inferred. In Nova Scotia the system 

 attains a thickness of some 13,000 feet. 



West of the Great Plains. — Formations made during the period 

 when the Pennsylvanian system was accumulating in the east are 



1 Reports of the Geol. Surv. of Illinois and geological map of Illinois. 



2 Reports of the Geol. Surv. of Iowa and geological map of Iowa. 



3 Coal-ate folio, U. S. Geol. Surv. 



4 Shaler, Woodworth and Foerste, Geology of the Narragansett Basin, Mono. 

 XXXIII, U. S. Geol. Surv. 



5 Emerson and Perry, Geology of Worcester, Mass ; also Perry, Jour. Geol., Vol. 

 XII, p. 7 



