C.—GEOLOGY 51 
possess a distinctive composition, independently of the materials from 
which it was derived. The earlier microscopic observations at once 
limited this idea by demonstrating the presence of plant remains which 
retained their organised structure; but the ‘ uniform brown substance,’ 
which Hutton had observed to form so much of the coal, clearly appealed 
to many observers as the essential feature, and many references to the 
* coal substance’ seem to be more or less clearly identified with it. The 
foremost question in coal petrology has been, in fact, the nature of this 
brown substance—in particular, as to whether it is, in more modern 
phrase, a colloidal precipitate, or whether it represents actual fragments 
of plant material. Since it forms probably quite 75 per cent. of all our 
common coal, this question is of the first importance. As Hutton ob- 
served, it is this substance which forms the general mass of the ‘ bright 
coal. 
All recent workers have drawn attention largely to this dominating 
material. E.C. Jeffrey named it ‘ lignitoid material.’ He regards it as 
representing pieces of plant tissue, largely woody, in which all trace of 
the original organisation has been destroyed by decay. Thiessen, who 
approached the study of the structure of bituminous coals by way of an 
extensive examination of lignites, in which the structure is more easily 
seen, differed from Jeffrey chiefly in his belief that the structure of the 
original plant material is rarely quite obliterated, and that it can nearly 
always be detected if the sections and the microscopic technique be 
sufficiently good. He named the material ‘anthraxylon.’ 
The recent trend of work and discussion on this important part of the 
coal has been much influenced by the writings of Dr. Marie Stopes. In 
1919 she essayed a classification of the types of coal substance which can 
be distinguished by eye in an ordinary bituminous seam, and gave some 
account of the constitution of each type as determined by microscopic 
examination. She emphasised again the laminated character of the 
seam, and the fact that the laminz consist of different types of coal 
which can be separated for examination. While earlier writers had 
usually been content to describe the coal as divisible into ‘ bright’ and 
‘dull’ layers, together with occasional bands of ‘ mineral charcoal’ or 
‘mother of coal,’ she directed attention to the additional fact that the 
‘bright’ coal might be separated into two portions. ‘The general mass 
of the bright substance has a just perceptible fine lamination which gives 
it a silky sheen ; but interbanded with it are many thin layers which at 
once strike the eye by the mirror-like reflection from their perfect cleavage 
surfaces. The same observation was undoubtedly made many times 
before, but failed to attract notice, in the same way that the whole matter 
of the distinctive character of the various laminz which make up the seam 
received only casual attention from time to time. Dr. Stopes was the 
first to apply distinctive names to the different types of laminz. She 
adopted the French fusain to replace the questionable English term 
“mineral charcoal,’ and devised corresponding terms for the other types 
of coal: durain for the true dull bands; clarain for the ordinary silky 
bright coal ; and vitrain for the brilliant glassy-looking substance. 
Not all the weight of Shakespeare’s authority can alter the fact that 
