April, 1841.] 11 



In most bituminous coals, and in not a few anthracites, the 

 "cleavage of the laminae," or what I have chosen to call surfaces 

 of deposition, are sufficiently distinct, and afford ready partings to 

 separate masses into small pieces. In some of the harder anthra- 

 cites, however, these surfaces are nearly obliterated, being dis- 

 tinguishable only by different shades of black. The actual cleava- 

 ges of the coal, in such instances, seldom take place along the sur- 

 face of deposition ; but on igniting the specimen, we may generally 

 obtain partings in those natural seams. I exhibit an example in 

 coal of Hazleton. 



The regular slines also, in anthracite, are sometimes so far ob- 

 literated as to be only developed by strong heat or partial combus- 

 tion. They are then shown by the thin, white, shining lamina? of 

 earthy matter, which mark two opposite sides of a lump of half 

 burnt coal. 



The absolute direction of the cleat is very various. At the Lau- 

 rel Hill mines, in Hazle creek valley, it is believed to be about 

 north 80 east. 



In some beds of coal which I discovered and examined on the 

 West Branch of the Susquehanna, it is due east and west by com- 

 pass. 



In the Middleton mine coal, in the Northerly part of England, it 

 is from N. 20 West to N. 32 W. 



The second, or " short cleat," in opposition to the " long cleat," 

 which extends for great distances, is the cross parting already 

 spoken of, and not unfrequently runs perpendicularly to the direc- 

 tions of both the " cleavage of the lamina? and to the long cleat." 

 This is seen both in bituminous coals and anthracites. 



Another circumstance to which I would refer, as indicative of the 

 similarity of origin and correspondence in character, between bi- 

 tuminous coals and anthracites, is the correspondence of the two, 

 in respect to the composition of the ashes of the two kinds. Silica, 

 alumina, oxide of iron, with small amounts of lime, magnesia, and 

 occasionally of oxide of manganese, are the ingredients of the ashes 

 of both the kinds of coal. The proportions vary, not only in the 

 different kinds of coal, but also in the several plies of the same bed, 

 both in the bituminous and anthracite districts. In the anthracite, 

 the diversity of composition is marked by the colour of the different 

 streaks after partial incineration. 



