SECTIONAL TRANSACTIONS.—C. 373 
chemical criterion could be a measure of ‘ rank,’ but at most an index. 
Chemists were not agreed as to the index of ‘ rank.’ The amount of oxygen, 
carbon, volatile matter, the calorific value and recently the reactivity had 
been proposed. All these are simply related to each other when the hydrogen 
is constant. Since the hydrogen of the orthohydrous coals varies only 
between narrow limits (5 to 6 per cent.), any of the proposed indices will 
give the same order of rank approximately but not exactly. It appeared 
that the geologist and chemist were each waiting for the other to produce 
a true measure of rank. In the speaker’s opinion it must come from the 
geo-physicist. The choice of a chemical index was more or less arbitrary 
and must remain so until we have a quantitative knowledge of the factors 
which produce metamorphism. 
Dr. A. RAISTRICK. 
In my work on the microspores of coal it has been necessary to subject 
a very wide range of coals to drastic chemical treatment, and I have had the 
opportunity of noting the very close correspondence of the responsiveness 
of acoal and itsrank. A recent investigation of the Busty seam of Durham 
has involved the chemical treatment of samples of that seam from over 
fifty localities fairly evenly distributed over the whole coalfield and varying 
in volatile content from 27 per cent. to 39 per cent. The treatment of all 
samples was standardised, both quantitatively and for time-temperature, 
and consisted briefly in oxidation of the coal with Schulz’s solution, followed 
by extraction with caustic potash. The types and proportions of types of 
microspores obtained proved similar in all samples, and enabled direct 
correlations to be made, but the quantity of spore material varied very 
markedly with the rank of the coal. ‘The coals of less than 30 per cent. 
volatiles have yielded less than one-tenth the amount of spore material 
given by coals above 35 per cent. volatiles. While the extracts from high 
rank coals need from four to six times as much washing as those from low 
ranks, there is much to suggest that fewer spores are present in the high rank 
coals, as prolonged or modified treatment has in no case enabled a greater 
yield of spores to be obtained. This work suggests that there are two 
factors connected with rank: (a) a very different response to chemical 
treatment, and (6) possibly a much smaller proportion of spore material in 
coals of high rank. 
Mr. C. E. MarsHa.t. 
Among the features of structure which can be compared in different coals 
perhaps the most obvious is the widely varied condition of preservation of 
the plant tissues. An examination of such tissues from coals of various 
ages and ranks, therefore, should reveal whether or not there is any diversity 
in their mode of preservation which could be correlated with the rank of 
the coals. As a result of such an examination applied to coals of different 
tanks (ranging from peat to semi-anthracite) and of various ages (from 
Carboniferous to Glacial) it has been found that the types of preservation 
of the cell structures in coals of bituminous and higher ranks are entirely 
similar to those of the earlier stages. In other words, the same types of cell 
preservations are common to coals of all ranks and ages. Consequently 
it seems certain that the structure of the coal is determined in the very early 
stages of its formation, that geological influences cannot have much effect 
upon the petrography of the coal seam, and that rank is not appreciably 
influenced by the degree of degradation achieved in the coal swamp. 
