THE PENNSYLVANIAN PERIOD. 



577 



anthracite (Figs. 264-267), while in the central, and in most of the 

 western coal-fields of Pennsylvanian age, where the strata are nearly 



L. 



-j 



J 



/ 



r 



\ 



L. 



J 



y 



> 



Fig. 263. — Map showing the areas of anthracite coal in Pennsylvania. 



horizontal or but slightly deformed (Figs. 255, 256 and 267 to 271), 

 and altogether non-metamorphic, the coal is bituminous or soft. In 

 Arkansas 1 where the strata have been subject to some, but not to 

 extreme dynamic action, there is coal which is semi-anthracitic. Where 

 the metamorphism of the associated rock has been extensive, the 

 coal has gone beyond the anthracitic stage and has become graphitic. 





Fig. 264. — Section across Panther Creek basin in the anthracite region of Pennsyl- 

 vania, showing the position of the strata and the coal beds. (Stoek, U. S. Geol 

 Surv.) 



Thus in Rhode Island, where the strata have been highly metamor- 

 phosed, the coal is highly anthracitic, or even semi-graphitic. 2 



Anthracite coal is also found in some places (though not in the 

 Coal Measures of the United States) in contact with dikes, in just the 



1 Ann. Rept. Ark. Geol. Surv. 1888, Vol. III. 



2 Geology of the Narragansett Basin, Mono. XXXIII, U. S. Geol. Surv. 



