474 



Dr. M. C. Stopes. On the Four Visible 



powdery, readily detachable, somewhat fibrous strands. The orientation of 

 the fibrous structure tends to be lengthways in relation to each wedge, and 

 the various wedges on a bedding plane lie at various angles to each other, so 

 that in any given light some appear dull and some glisten according to the 

 direction the light catches the fibres. 



The fusain is readily separated from the rest of the coal (which is all 

 firmer than it in texture) by delicate scraping with a blunt knife, when the 

 short, fibrous strands and small, sharp-pointed, irregular fragments fail freely 

 on to a paper laid so as to catch them. 



Where, as may happen, a thick wedge of fusain is contiguous with a true 

 vitrain band, the fusain may appear as though, embedded or sunk in the 

 vitrain (cf. the text-fig., 2 /). The fusain can then be entirely scooped out, 

 leaving exposed on the vitrain the hollow in which it lay, the surface of this 

 vitrain hollow being curved and smooth. The contact surfaces of both clarain 

 and durain with fusain, however, are much less precise, and an impression of 

 the fibres of the fusain is generally left on the harder durain or clarain after 

 all the friable detachable fibres of the fusain have been removed. 



Durain occurs generally as bands of very variable thickness, and when 

 seen in a face at right angles to the bedding plane, they appear parallel to it, 

 though, if traced far enough, they generally reveal their ultimately lenticular 

 shape. Wider bands of comparatively pure durain are less common, but 

 bands, 2, 3, or more inches thick are often sharply dififerentiated from the 

 adjacent streaky bright clarain. 



Durain is hard, with a close, firm texture, which appears rather granular 

 even to the naked eye. However straight the break across it, the broken 

 face is never truly smooth, but, if looked at closely, always has a finely lumpy 

 or matte surface (see Plate 11, fig. 1). Generally, even in the dullest of durain 

 bands a few (or many) flecks or hair-like streaks of bright coal are to 

 be seen. 



The intercalation of narrow bands of durain and clarain tends to increase 

 at the junction of the broad " duU " and the broad " bright " bands, so that 

 there is no large surface of contact between them which is sharp cut and well 

 defined, even the purest clarain and the purest durain tend to have ravelled 

 edges, which interlock (see text-fig. 4, junction between c and d). 



Clarain occurs generally as bands of very variable thickness, and when seen 

 in a face at right angles to the bedding plane they appear parallel to it. 

 Like durain bands, they are ultimately widely extended lenticular masses. 

 Clarain, even when considerably streaked with durain, has a definite and 

 smooth surface when broken at right angles to the bedding plane, and these 

 faces have a pronounced gloss or shine. This surface lustre is seen to be 



