ANTHRACITE COAL MEASURES. 



241 



nes northwest of the Alleghany Mountains. These 

 bluish shales contain, though not abundantly, very 

 beautiful impressions of ferns and stems of cala- 

 mites, and in the lower portions of the deposite the 

 stems and leaves of other curious vegetable fossils, 

 as iepidudendron, sigillaria, and cactus. 



" In the immediate vicinity of the seams of coal, 

 these shales become more or less carbonaceous, and 

 acquire a darker colour and a more purely argilla- 

 ceous texture. On such the miners bestow the 

 name of coal slates. These slates, it is generally 

 thought, differ materially in appearance and com- 

 position, according as they lie above or beneath 

 the coal-seams. The overlying slate often con- 

 tains innumerable extremely thin sheets of pure an- 

 thracite, minutely interlammated with equally deli- 

 cate layers of slate. This is technically called hone 

 coal, and is frequently mistaken by the inexperi- 

 enced for pure anthracite, though it is easily recog- 

 nised by its tendency to split into parallel layers, 

 or by the number of the ferns and other delicate 

 vegetable impressions usually found in it. The un- 

 derlying slate is, on the contrary, of a much tougher 

 consistence, and of a more regular and well-defined 

 fracture, breaking into firm splintery masses in- 

 stead of loosely aggregated scales. 



" These slates, in contact with the coal-beds, vary 

 from one to twenty or even thirty feet in thickness, 

 and not unfrequently occupy the entire space be- 

 tween two contiguous coal-seams." 



We have already stated that the anthracite beds 

 of Worcester (Massachusetts) occur in mica slate ; 

 those in Mansfield, Middleborough, Wrentham, &c., 

 occur in gray wacke, as well as those of Cumberland 

 in Rhode Island. 



The coal measures, as exhibited in the following 

 sections, it will be understood, belong to the lower 

 secondary rocks ; that is, they lie next to the tran- 

 sition rocks, and, according to some of our best 

 T 



