COAL. 35 



tion, viz. at right angles to the lamellae, contain the most hitumen, and are 

 the best for the production of gas. 



Haidinger, in his translation of Mohs's work on Mineralogy, makes the 

 following observations on coal : 



" Bituminous Mineral Coal. No regular form or structure ; fracture con- 

 choid al, uneven ; lustre resinous, more or less distinct ; colour black or brown, 

 passing, in earthy varieties, into grayish tints ; streak unchanged, except that 

 it sometimes becomes shining-opake : sectile in different degrees : hardness 

 = 1-0 to 2*5. Sp. gr. = 1-223, moor coal from Teplitz ; = 1*270, common 

 brown coal from Eibiswald, in Stiria ; = 1*271, black coal from Newcastle 

 = 1-288, bituminous wood ; = 1*329, common brown coal from Leoben, in 

 Stiria ; = 1 '423, cannel coal from Wigan in Lancashire. 



" Compound Varieties. Massive ; composition lamellar ; faces of composi- 

 tion smooth and even, different gradations ; granular texture often impalpable, 

 and then fracture is uneven, even, or flat conchoidal. Lignifonn shapes, 

 the structure of which resembles that of wood, sometimes very distinct, but 

 often obliterated, with the exception of some slight traces : fracture then be- 

 comes conchoidal, particularly across the fibres. There are some earthy 

 varieties of a loose friable texture." 



In the species of bituminous mineral coal are comprised the Brown and 

 Black Coal of Werner, excepting the Columnar Coal, which belongs to the 

 new bituminous class (Mohs, vol. iii. p. 62) ; these two kinds, however, and 

 still more the varieties they contain, are very difficult to be distinguished : 

 colour, structure, and the kind of lustre which depends upon the latter, are 

 almost all that remain to mark their distinction. The colour of Brown Coal, 

 as the name imports, is brown ; it possesses a ligneous structure, or consists of 

 earthy particles : the colour of Black Coal is black, not inclining to brown, and 

 it does not possess the structure of wood. The varieties of brown coal are the 

 following : Bituminous Wood, or Bovey coal, which presents a ligneous tex- 

 ture, and very seldom anything like conchoidal fracture, imperfect and without 

 lustre. Earthy Coal, consisting of loose friable particles. Moor Coal, or trape- 

 zoidal brown coal, distinguished by the absence of ligneous structure, by the 

 property of bursting and splitting into angular fragments when removed from 

 its original repository, and the low degree of lustre upon its imperfect con- 

 choidal fracture. Common Brown Coal, which, though it shows traces of lig- 

 neous texture, is of a more firm consistency than the rest of the varieties, and 



F2 



