62 PHYSIOGRAPHY. 



Bituminous Coal. 



slight traces, when the fracture becomes conchoidal across 

 the fibres. There are some earthy varieties of a loose fri- 

 able texture. 



1. The present species is treated by some writers as forming four sep- 

 arate species : viz. Brown Coal, Black Coal, Cannel Coal and Jet ; 

 and the two first mentioned varieties have been again divided into seve- 

 ral sub-species. The color of Brown Coal is brown, as its name imports. 

 It possesses a ligneous structure, or consists of earthy particles. Its va- 

 rieties are as follows : Bituminous Wood, which presents a ligneous 

 texture, and very seldom any thing like a conchoidal fracture, and is 

 without lustre ; Earthy Coal, consisting of loose friable particles ; Moor 

 Coal, or Trapezoidal Brown Coal, distinguished by the want of ligne- 

 ous structure, and by the property of bursting and splitting into angular 

 fragments, when removed from its original repository ; Common Brown 

 Coal, which, though it still shows traces of ligneous texture, is of a more 

 firm consistency than the rest of the varieties, and possesses higher de- 

 grees of lustre upon its more perfect conchoidal fracture. The color of 

 Black Coal is black, without inclining to brown, and it is destitute of the 

 ligneous texture. Some of its varieties immediately join those of Brown 

 Coal. They are : Pitch Coal, of a velvet black color, generally inclin- 

 ing to brown, strong lustre, and presenting in every direction a large and 

 perfect conchoidal fracture ; Slate Coal, possessing a more or less coarse, 

 slaty structure, which, however, seems to be rather a kind of lamellar 

 composition, than real fracture ; Foliated Coal, which is similarly com- 

 pounded, only the laminae are thinner ; Coarse Coal has a composition 

 resembling it, only the component particles are smaller, and approach to 

 a granular appearance. Cannel Coal is without visible composition, 

 and has a flat conchoidal fracture in every direction, but with little lus- 

 tre, by which it is distinguished from Pitch Coal. It most resembles the 

 Moor Coal, but the difference in their specific gravity is greater than be- 

 tween almost any other two varieties of coal. Jet occurs in elongated 

 reniform masses, and sometimes in the shape of branches with a regular 

 woody structure. Its lustre is brilliant, and its fracture perfectly con- 

 choidal. All these kinds, however, are united by numerous transitions, 

 so that it continually becomes doubtful to which of them we should refer 

 certain specimens, though thoy are undoubtedly Bituminous Coal. 



2. Bituminous Coal is more or less easily inflammable, and burns with 

 flame and a bituminous smell. Several varieties become soft; and others 



