MODE III. COAL. 53 1 



and probably, on a chemical analysis, these 

 kinds of coal would be found to yield a small 

 portion of iron and sulphur. 



The structure of coal, as already mentioned, 

 may be regarded as universally schistose: and it 

 is believed that even the columnar may be con- 

 sidered on a large scale, in the same point of 

 view, that is, the columns are horizontal, and 

 piled like billets of wood on each other. The 

 small columnar kind found in Scotland, consists 

 of little columns, about half an inch in diame- 

 ter, and a few inches in length, united in a com- 

 mon base *. Its form seems to arise from the 

 ferruginous gangart, which envelopes, as in a 

 sheath, the little columns of coal; and it is like- 

 wise said to occur in a form merely schistose. 

 It is in fact so minute as rather to belong to li- 

 thology. The chief variations of coal can there- 

 fore only be classed as aspects. 



Aspect 1. Common coal. This substance is 

 only observable when it presents some remarkable 

 diversities, is accompanied with singular accidents, 

 or is brought from new regions. 



* Mr. Jameson, Dumf. 1(50, says it is found about four miles 

 from New Cumnock, Ayrshire, along with graphite, which is also 

 sometimes columnar. 



