i jo The Constituents of Banded Humic Coal. 
on heating, an essential feature in the production of large 
pieces of compact coke suitable for metallurgical purposes, 
depends on the presence of vitrain (and clarain). From the 
physical point of view, the durain and fusain present act as 
‘ inert ’ material which is bound together by the fusion of 
the bright coal. Apart from special preliminary treatments, 
therefore, coals required for coking purposes must contain a 
sufficient proportion of vitrain and clarain. On the other 
hand, a coal may fuse so readily that it is advantageous to 
blend it with a certain proportion of coal which is richer in 
durain and fusain. Again, inferior coals may be pressed into 
service by blending. 
The following brief notes may be given in explanation 
of the Table : — 
(1) The terms vitrain, clarain, durain and fusain are 
based on the macroscopic physical characters of the ingredients. 
Thiessen’s terms, anthraxylon and attritus, are based upon 
the origin of the material which went to form the ingredients. 
With the exception of fusain, Thiessen’s terms are not strictly 
equivalent to Dr. Stopes’ terms as here shown. Anthraxylon 
represents coaly matter derived from botanically homogeneous 
and attritus from botanically heterogeneous debris. Fusain 
is usually, though not invariably, composed of homogeneous 
material ; durain is always of heterogeneous origin ; clarain 
is usually heterogeneous ; vitrain commonly, but not always, 
homogeneous. A lenticle of vitrain often represents a single 
plant fragment, but sometimes consists of the remains of 
miscellaneous tissues. 1 
(2) As was first pointed out by Dr. John Pringle, 2 the 
coaly layer investing stems fossilised in shales and in sand- 
stones always consists of vitrain. 
(3) The term ‘ dice ’ applies chiefly to vitrain (which 
tends to break up into small dice-like cubes), but clarain has 
also been included under the name. 3 
(4) Glanzkohle may also refer to anthracite. 
(5) Clarain forms the bulk of most British seams of humic 
coal. The distinction originally drawn between vitrain (as 
structureless) and clarain (as containing plant structures, 
visible in thin sections under the microscope) has now broken 
down (see below). The great similarity between vitrain and 
the brighter clarains in chemical composition and properties 
1 Seyler, C. A., ‘ Banded Bituminous Coal,’ Fuel, Vol. 5, 1926, p. 182. 
Thiessen, R. and W. Francis, ‘Terminology in Coal Research,’ ibid., 
Vol. 8, 1929, p. 385. 
2 Pringle, J., ‘ On the Origin of Bright Laminae in Coal,’ Trans. 
Edinb. Geol. Soc., Vol. X, 1911, pp. 30-37. Lomax, J., Colliery 
Guardian, Vol. 129, pp. 514-516. 
3 Gresley, W. S., Trans. Manchester Geol. Soc., Vol. 21, 1892, p. 520. 
The Naturalist 
