Ingredients in Banded Bituminous Coal. 481, 



(in which it resembles clarain) and its structureless and uniform texture, in 

 which it differs from all other parts of coal. As it is technically difficult 

 (my own cutter and Mr. Lomax, to whom I sent samples, find it impossible) 

 to grind down this substance to absolute uniform thickness over the whole 

 area of the section, the section has areas shading from pale gold to ruddy 

 brown, but these obviously depend on the varying thickness of the slice 

 examined : the mass ' is, uniform in its structureless nature. Plate 12, 

 fig. 4 (coloured), shows the yellowish to dark amber colour of the uniform 

 mass. Scratches show up on the surface very annoyingly, and are due to 

 minute irregularities even in the finest polishing stone ; they are unduly 

 conspicuous in photos., but when the eye examines a number of sections it 

 readily detects the essential uniformity of the vitrain, and its structureless 

 nature, as of a hardened glue or jelly. In it may be seen an occasional 

 isolated spore, or a fine streak of durain may have been included, but if the 

 purest, most brilliant vitrain is selected, it is essentially homogeneous. The 

 illustration given on Plate 12, fig. 4 (coloured), illustrates this, though, 

 imperfectly, and offers a contrast to the standard sections of durain and 

 clarain (Plate 12, figs. 2 and 3). 



. There is, consequently, in pure vitrain no banding or differentiation of parts 

 in relation to the bedding plane of the deposit, though any individual mass of 

 vitrain generally itself forms a horizontally extended band, lying parallel to 

 the bedding of the coal. 



The original thesis of this paper is borne out in the above details of these 

 very various observations, and I think we may now see in ordinary bituminous 

 banded coal four recognisably distinct and differentiable ingredients, for 

 which I propose the names fusain, durain, clarain, and vitrain. These four, 

 though difficult to separate completely, and ever tending to be interbanded 

 and to penetrate each other, can yet, in most ordinary banded seams, be 

 recognised by the naked eye, locally pure, and obtained by hand separation 

 nearly pure. Such separated samples from a few adjacent inches of coal 

 show marked differences : (i) in their effect on sensitive plates, (ii) in their 

 behaviour with various solutions, (iii) in the quantity and character of the 

 debris they yield under treatment, (iv) in the microscopic details of this deh'is, 

 (v) in the microscopic appearance of the substances in thin, ground, untreated 

 sections. Further, in their chemical analyses, distillation products, and so 

 on they differ ; but these features will be dealt with by Dr. Wheeler. 



The above data apply particularly to the well-banded, relatively undis- 

 turbed coals of the Midlands, of which the Hamstead Colliery yields 

 excellent examples. In some other seams, particularly those visibly affected 



