C.—GEOLOGY 53 
Two views regarding the nature of the ‘uniform brown substance.’— 
Thus the ‘uniform brown substance’ for the most part, at least, 
represents portions of plant tissue with their organised structures ex- 
quisitely preserved. But the reservation in the preceding paragraph was 
necessitated by the fact that with any technique yet devised, it has been 
impossible to demonstrate that all this material possesses structure ; and 
this fact is frequently seized upon in discussions of the two views which 
are held regarding the essential nature of the brown substance as a whole. 
There are those who regard it as made up entirely of plant fragments, each of 
which now consists only of the remains of the organic substance of which 
that particular plant fragment was originally composed. ‘The alternative 
view is that a large part of the substance of the original vegetation was 
reduced by early decay to the condition of a true fluid, some of which 
was absorbed into those plant fragments which retained their organisation, 
while other portions of the fluid may have solidified as a truly structureless 
gel, and acted as a cement to the whole mass. ‘The latter view is almost 
universally held among Continental workers, and these accordingly are 
disposed to interpret the ‘ structureless’ material as evidence of such a 
gel. Whatever may be the amount of truth in this latter hypothesis— 
and there is considerable evidence that it applies in some cases—it is 
absolutely unquestionable that the plant remains which now form this 
translucent coal substance have been rendered jelly-like, whether by 
their own decay or by absorption of extraneous material. In nearly all 
cases cell-walls which were clearly rigid have been flattened and folded 
without rupture. Often the entire tissue has been contorted into the 
most fantastic forms, but still remains unbroken. 
So far as appearance is any guide to composition—and there is good 
ground for the belief that it does give some indication—there is little 
reason to suppose that the essential nature of this substance is very differ- 
ent whether the plant-structure be discernible or not. Differences we 
must expect to find when sufficiently detailed chemical examination is 
applied, and it will be of the greatest interest to discover how far they 
are affected by the nature of the original plant material. But for the 
present, all our evidence points to a remarkable general uniformity. 
The discussion of this question is obviously a matter for the chemist, 
but reference to only two of the distinctive qualities of this substance may 
be made, as sufficiently significant. Ifthe purest substance, as represented 
by vitrain, be examined, the ash-content is always found to be amazingly 
low. Not only is it a mere fraction of that present in the rest of the coal 
substance, but it is much below that in any average aggregate of modern 
plant materials. There is no reason to suppose that the vegetation of the 
coal-forests was abnormal in its content of inorganic matter, so we must 
presume either that the inorganic content of this part of the coal has been 
reduced, by leaching out, or that there has been a very large addition of 
pure organic substance. Secondly, this material shows extremely little 
variation in its organic composition, as compared with the other con- 
stituents of the coal. While the hydrogen content, for example, in the 
different ingredients of a single block of bituminous coal may be found to 
range from 3} to 8 per cent., the variation among samples of vitrain from 
