Ingredients in Banded Bituminous Goal. 



479 



material in the coal sections, among which are recognised various plant 

 tissues, resin bodies and other things in the coal. 



Many carefully marked banded pieces of coal, and also small pieces com- 

 posed of each separate ingredient as pure as could be obtained were cut 

 into sections in the course of the present work, and from them the persistence 

 of certain characteristics in each of the four types was made evident 

 Describing the four ingredients now recognised in the order hitherto 

 followed : — 



The fusain (which, though friable, at times forms patches or lenticels in 

 the coal, from which more or less complete sections can be cut) is almost 

 black, opaque, and when it shows the cellular structure of the wood from 

 which it was formed, it reveals the walls as much thickened and the cell 

 lumina as being generally empty. When the section is approximately at 

 right angles to the direction of the wood fibre, an appearance as shown in 

 Plate 12, fig. 1 (coloured), results. This illustration, though in natural colours, 

 looks almost black and white, save at s where is the gleam of an adjacent 

 spore, showing the colour contrast between fusain and the other portions of 

 the coal in section. 



The botanical nature of the various plant fragments sometimes identifiable 

 in the fusain does not concern us here ; their general optical effect varies but 

 little whatever species they are. 



The durain being firm and hard in texture is more easily cut and ground 

 than fusain, but as it tends to be rather granular, it is more difficult to finish 

 finely than the more coherent and softer clarain. Sections show a granular 

 matrix of roundish or polyhedral fragments, the majority of which are 

 blackish and opaque. The granules are closely packed and form a coherent 

 mass, but mixed with them are the most characteristic spore exines. These 

 may be whole or in fragments. The macrospores are most conspicuous, and 

 their very thick exines are clear and brilliantly coloured, almost red, though 

 when thinner they are reddish gold to pale gold or amber colour. In durain 

 the ground mass of rather opaque granules, and the large clear macrospore 

 exines tend to preponderate, see Plate 12, fig. 2 (coloured). There may or may 

 not be a number of small microspores mingled with the granules forming the 

 bulk of the durain. Throughout the texture of the less pure, streaked durain 

 are seen in section small, clear, generally lenticular bands or flecks of a more 

 golden colour. These are the streaks of clarain which so commonly lie 

 interbedded with the durain (c/. p. 474). The purer the durain the fewer of 

 these clear patches are to be seen in the section. These should be distin- 

 guished from certain other light coloured bodies sometimes to be seen in the 

 durain, viz., the supposed " resin " bodies and other small distinctive 



