54 SECTIONAL ADDRESSES 
the same block will rarely exceed a twentieth of that amount. It is 
because most coals consist mainly of this substance that they differ so 
little from one another. Prof. Wheeler and his colleagues have shown 
that it is mainly composed of ulmin compounds. 
If, now, I have seemed to dwell unduly on this ‘ uniform brown 
substance,’ which we see practically pure in the bands of vitrain and some- 
what adulterated in clarain, I must repeat that it is by far the most import- 
ant constituent of coal. If anything deserves the name of ‘ coal substance’ 
it is this, though there are countless reasons why such a designation 
would be most undesirable. But it is none the less unfortunate, in the 
interests of clarity, that we have no universally accepted term by which to 
denote it. It is the ‘anthraxylon’ of Thiessen and the ‘ lignitoid’ of 
Jeffrey. Both these terms offend the more scrupulous by their implication 
that ‘ wood ’ is the only parent substance ; which is far from being the 
case. Some workers have suggested the restriction of those terms to 
such examples as can be shown microscopically to have been formed from 
wood, coupled with the introduction of such terms as ‘ suberitoid’ for 
examples in which ‘ bark’ can be shown to be the parent material, and 
so on for other cases. There is grave danger of confusion and misunder- 
standing of much valuable work in a welter of conflicting terminology. 
Dr. Stopes has recently tried to cut the Gordian knot by devising a set 
of co-ordinated terms which will cover all the possible cases. But the 
prime need of the moment is clear recognition of the general similarity 
of this substance irrespective of the plant tissue out of which or in which 
it has been formed. A term is required which has no botanical implica- 
tions. In the vitrain bands we see the substance in its most tangible 
form. But the term vitrain cannot well be applied to the substance 
itself, since it is also the major component of the clarain bands. The 
term vitrinite, however, suggested by Dr. Stopes, offers an escape from 
this difficulty, while recalling the fact that in vitrain we have the 
substance in its purest form. I shall therefore use this term in the 
sequel. 
The other Components of Coal.—We must now take stock of the other 
materials which go to the make-up of an ordinary coal seam. Though 
they are subsidiary in amount to the vitrinite in most portions of the 
seam, it is the character and varying quantity of these other materials 
which primarily differentiate the quality of the coals. 
Most conspicuous and familiar is the ‘ mineral charcoal’ or fusain. 
This illustrates at once the fact that in some cases the mode of preserva- 
tion of the plant-substance may be of greater import than its original 
nature. The fusain is usually woody tissue, clearly identical originally 
with much of that which has been converted into vitrinite. But how 
different in its present form! Devoid of any organic substance in its 
cell-cavities ; every cell-wall so brittle as to break at a touch; always 
extremely low in its content of hydrogen and oxygen, and correspondingly 
high in carbon. Physically and chemically it stands in the strongest 
possible contrast. On account of its porous nature it has commonly 
formed the receptacle for much of the mineral matter which has been 
deposited from solution in the coal, and is consequently a great carrier 
