48 SECTIONAL ADDRESSES 
This is, in fact, a fair indication of the state of knowledge regarding the 
structure of coals in general, up to some thirty years ago. Enough was 
known from such investigations as those, for example, of Grand’ Eury on 
the coals of St. Etienne, to indicate that different coals might have been 
formed from substantially different materials, but far too little information 
was available to enable anyone to determine just how far the conspicuous 
differences in composition between the coals were due to that cause. There 
was complete uncertainty whether even the major differences were deter- 
mined during the accumulation of the deposit, by the kind of plant 
materials concerned and by their state of decay; or whether the chief 
factor was the effect of physical forces brought to bear on the deposit after 
its burial in the crust. During the past thirty years the state of knowledge 
in this matter has undergone a complete change; but the investigators 
responsible for the change have, for the most part, been palzobotanists and 
fuel technologists rather than pure geologists. The results of their work 
have not for the most part appeared in the ordinary geological journals, 
and their geological implications have consequently not received general 
attention. 
Early Microscopic Studies——The earlier uncertainty regarding the 
structure of coal was due to the extreme difficulty of preparing slices 
sufficiently thin to be in any degree translucent, and so to permit of 
microscopic examination. Nevertheless, so far back as 1831, Henry 
Witham had prepared sections in which he had seen plant structure, and 
in January 1833, a paper was read before the Geological Society of London, 
by William Hutton, based on the examination of a considerable collection 
of thin sections. This was, unfortunately, published in brief abstract 
only, but the original manuscript, at present in my possession, shows that 
he had observed most of the features which were noted by later observers 
until very recent times. The paper is accompanied by nine illustrations 
in colour, which greatly assist in the interpretation of his descriptions. 
He notes three types of coal in the Newcastle district, each with a character- 
istic structure. The first and most abundant is (to quote his words), the 
‘fine caking coal,’ which consists of ‘a mahogany-brown coloured sub- 
stance, compact and uniform ; mixed and entangled in this are to be seen 
portions retaining the fine reticulations of the original plants.’ From its 
‘ more or less perfect rhomboidal fracture, when broken’ it is ‘ seen to be a 
crystalline compound ; the parts composing it must have been in a state of 
solution. . . .’ ‘ Along with this there are generally a number of curious 
elongate cells, filled with a light wine-yellow coloured substance .. .’ 
which is ‘ undoubtedly a bituminous compound . . . and may be volatil- 
ised by a gentle heat so as to leave the cells empty without the surrounding 
coal being altered ’ [a remarkable observation]. These cells are, of course, 
the spores, and in the light of subsequent discussion, it is interesting to 
note that the material of which they consist is later described as yellow 
resin. ‘The second variety, or ‘ slate coal,’ is described as largely made 
up of these ‘ elongate cells’ and consists also ‘ of a congeries of other 
smaller cells . . . similarly filled with yellow resin’ [the microspores]. 
The third variety is the Cannel, Splint or Parrot coal, which is ‘ totally 
devoid of crystalline structure’ and displays an ‘ almost uniform series 
