Ingredients in Banded Bituminous Coal. 



473 



whole its- more wedge-shaped portions tend to lie so as to be most apparent 

 on the surfaces which are split parallel to the bedding. The appearance of 

 fusain has very often been described. 



The fourth ingredient, the vitrain or brilliant bands, have been less con- 

 sidered in the past, but are, as a matter of fact, particularly interesting. 

 These brilliant bands, in a favourable sample, are very definitely deliminated 

 from the rest of the coal, much more so than are either tlie ordinary bright 

 clarain or the dull durain from each other, which, owing to the finely 

 lamellar nature of the coal in which they are interlarded, are sometimes hard 

 to separate. The true vitrain, however, generally forms a very definite and 

 often sharply straight-eut band, varying from 2 to 6 or 8 mm. thick. There 

 are, of course, brilliant streaks of smaller size, down to almost hair-like 

 flecks. The larger, however, are the more typical vitrain zones. They are 

 notably less numerous and less in quantity in most coals than are the 

 ordinary glossy bright clarain, and in some coals are scarcely to be found. 

 They should be carefully distinguished from the very glossy almost vitreous 

 thick zones of bright coal sometimes forming a great quantity of a seam, 

 which, however bright, will always show streakiness however subdued. A 

 true piece of pure vitrain is not streaky even with a magnifying glass. 



In studying minutely the four different portions of a coal, one point should 

 be borne in mind concerning the samples used ; and that is, that they should 

 all four be selected in situ, and as near to each other as possible. In the 

 mine, therefore, blocks should be cut out, each showing all four ingredients 

 as well differentiated and as nearly contiguous as possible. In this investi- 

 gation I worked with well banded blocks about 6 by 8 inches cube. In the 

 course of the work a large portion of each sample block is broken np, and the 

 zones where the intercalation of the " dull " and bright is very fine, are 

 useless for the isolation of the pure ingredients, as they cannot then be 

 separated by hand. It must be recognised further that both durain and 

 clarain can really never be got absolutely free from some streaks of each 

 other, but if in the durain there are only few and hair-like streaks of clarain, 

 and in the clarain only few and hair-like streaks of durain, they can serve 

 for all practical purposes as pure enough to indicate the relative character- 

 istics of really pure clarain and durain. With care, both fusain and vitrain 

 can be separated by hand from favourable samples in a really pure state. 



Tlie Appeo/rances of the Four Ingredients vjith the Nalxd Eye, i.e., their 

 Macroscopic Appearances. 

 Fusain occurs chiefly as patches and wedges, somewhat flattened parallel 

 •to the bedding plane, and often with rather square-cut ends. It consists of 



