CARBONIFEROUS AGE. 315 



1. Anthracite, which has high lustre and firmness, and burns with a 

 feeble flame, yielding little moisture, only traces of hydrocarbon gas, 

 and 84 to 95 per cent, of carbon. Specific gravity 1*3 to 1*8. Free- 

 burning anthracite, or Semi-anthracite, affords more flame, and of a 

 yellow color ; but still the proportion of volatile matters given off is 

 small, not exceeding 10 or 12 per cent. 



2. Bituminous Coal, having less firmness and lustre than anthracite, 

 and burning with an abundant yellow flame, the volatile combustible 

 substances afforded amounting usually to 25 or 35 per cent, of the 

 whole, and sometimes to 50 or 60 per cent. When these substances 

 are only 15 to 20 per cent, the coal is called semi-bituminous. There 

 are in fact all grades, between the true bituminous coal and the hardest 

 anthracite. Ordinary bituminous coal breaks with straight or irregular 

 lustrous surfaces : it sometimes divides into rectangular blocks, but 

 this is a result of a jointed structure, and never of crystallization. 

 Specific gravity mostly between 1*22 and 1.32. 



Some bituminous coals soften in the fire, becoming semi-pasty, and 

 then cake over ; such kinds are called caking coals. Others, undis- 

 tinguishable from the caking, both chemically and physically, are non- 

 caking. The " Block Coal," of Ohio, Indiana, and the neighboring 

 States, is of the non-caking kind. 



Cannel Coal (or Parrot Coal) is a variety of bituminous coal having 

 almost no lustre, a very fine texture, and a conchoidal fracture. It is 

 remarkable for the large proportion of volatile combustible material, 

 or mineral oil, which it yields. It received its name from its affording 

 a flame, like candles. Torbanite, a variety of cannel from Torbane 

 Hill, near Bathgate, in Scotland, yields over 60 per cent, of volatile 

 substances. 



Anthracite is the coal of Rhode Island, and of the areas in central Pennsylvania, 

 from the Pottsville or Schuylkill coal-field to the Lackawanna field (see map, page 310); 

 while the coal of Pittsburg, and of all the great coal-fields of the Interior basin, is 

 bituminous, excepting a small area in Arkansas. Anthracite belongs especially to 

 regions of upturned rocks, and bituminous coal to those where the beds are little dis- 

 turbed. In the area between the anthracite region of central Pennsylvania and the 

 bituminous of western, and farther south, the coal is semi-bituminous, as in Broad Top, 

 Pennsylvania, and the Cumberland coal-field, in western Maryland, the volatile matters 

 yielded by it being 15 to 20 per cent. The more western parts of the Anthracite coal- 

 fields afford the free-burning anthracite, or semi-anthracite; as atTrevorton, Shamokin, 

 and Birch Creek. 



Albertite, from the Nova Scotia Subcarboniferous (p. 296), and Grahamite, from the 

 Carboniferous in West Virginia (about twenty miles south of Parkersburg), are pitch- 

 like substances in aspect, constituting veins instead of beds, and not true coals. They 

 are supposed to have originated in distillation from some underlying carbonaceous 

 shales, which set free the material, as Wurtz observes, in a pasty state. Though like 

 asphaltum in color and lustre, they are not as fusible or as soluble in benzine or ether. 



The following are analyses of a few of the coals of the Carboniferous period. Others, 

 of albertite and of the more recent coal, called brown coal, and also of peat (the 

 ash excluded), are added for comparison. 



