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



by earth movements, the whole of the coal may have been slightly dislocated 

 and altered in minute steps, which, though not affecting either the bedding of 

 the roof and seam, or the coherence of the seam, may yet have destroyed the 

 interbanding of the four ingredients, as described above. Such coal may all 

 look very "bright," and may have only the streaks of fusain to represent the 

 " dull." An example of such a coal is seen in part of the Pentre seam of 

 South "Wales, in which one might search for long before finding a block with 

 anything but " bright " and fusain in it. 



Naturally, in order to obtain any light on the characters of these four 

 constituents, my endeavour was to obtain samples which contained the 

 ingredients in layers of sufficient size and purity for the respective substances 

 to be dealt with nearly pure. In most banded bituminous coals such samples 

 can be found if sought for, though they may be insufficient in bulk to handle 

 easily. The coal in bulk is generally composed of masses more intermingled, 

 so that small bands or lenticels of one or the other ingredient are interbedded, 

 and only separable by hand with great labour. 



In general, therefore, sections of coal which have formed the subject of the 

 investigations of previous workers will be found to contain at least two, and 

 probably more, of the four constituents so laboriously separated in the 

 present work. 



It may be useful, and is certainly in keeping with the attempt to obtain a 

 parallel to petrological knowledge, to give in a clear diagrammatic form the 

 orientation of the ingredients generally to be observed. The accompanying 

 four diagrams in the text (text-figs. 1-4) built up of conventional symbols 

 representing each of the four above-named ingredients, illustrate the kind of 

 distribution of the ingredients likely to occur ia sections, taken without 

 any special selection, from an average finely banded piece of bituminous coal. 



These diagrams actually represent a low scale of magnification, four 

 diameters, but, owing to the laminated nature of the coal, were more finely 

 laminated regions taken and multiplied five or even ten times this, it would 

 be possible to find areas which could justly be represented by the same 

 diagrams. 



An interesting feature to note is the comparatively straight line of 

 contact between vitrain and either clarain or durain adjacent to it, when cut 

 at right angles to the bedding plane ; while the contact surfaces between 

 clarain and durain tend to interlock in fine laminae. Fusain tends to form 

 irregular patches and wedges or lenses, which may have very small jutting 

 projections into either the durain or clarain (see text-fig.) and in the 

 vitrain may lie sunk in a comparatively smooth hollow (text-fig. 2). 



As these four ingredients of coal which I provisionally delineate are none 



