Reviews — Ingredients in Banded Bituminous Coal. 85 



may be many minor points in which the work is open to criticism from 

 those who belong to different schools of thought. A few palseo- 

 botanists may disagree with some of the nomenclature which is used, 

 or others may think that a genus in which they are interested has been 

 too scantily treated. But the fact remains that there are few men 

 who are willing or competent to undertake a task of the magnitude 

 which has now been so ably concluded, and all students of fossil 

 plants owe a considerable debt to the author. 



H. H. T. 



On the Four Visible Ingredients in Banded Bituminous 

 Coal: Studies in the Composition op Coal No. 1. By Marie 

 C. Stores, D.Sc, Ph.D. Proc. Roy. Soc. B., vol. xc, 1919, 

 pp. 470-87, with two plates and a text-figure. 



IN this paper the author proposes an extended scheme of subdivision 

 of the component parts of banded bituminous coal, which com- 

 prises terms more precisely defined than those formerly used, viz. : 

 " mineral charcoal," " dull coal," and " bright coal ". The new 

 classification is as follows : — 



(1) Fusain, " Mineral charcoal " or " Mother of coal ". 



(2) Durain, " dull coal." 



(3) Clarain ) c. ■. • i , , ,, 



(4) Vitrain j ^^^-^^^ ^^^^- 



Of these terms the first has been in use for some time in France, 

 but the last three are new. The ordinary appearance of the first 

 two is well known and needs no comment, but there seems to have 

 been considerable confusion in the past as to what exactly " bright 

 coal " is, some authors using the term in its broad sense and others 

 confining it to vitrain. Vitrain is a very brilliantly reflecting and 

 apparently homogeneous substance, with a conchoidal fracture, 

 and occurs generally as small lenses and thin streaks in the clarain. 

 Though the durain and clarain are predominant in the dull and 

 bright layers respectively, these layers are rarely pure, and the dull 

 layers generally contain thin streaks of clarain and the bright layers 

 enclose streaks of durain. Vitrain, however, is always pure and 

 shows no sign of banding. 



These four substances behave differently under both chemical 

 and microscopic examination. If pieces of them be placed in the 

 dark on a photographic plate the most intense image is obtained 

 from vitrain, one less intense from clarain, while that given by 

 durain is fainter still. Alcoholic potash causes vitrain to swell and 

 become soft, so that sections can be cut from it with a razor, but 

 makes the other three substances friable. Treatment with strong 

 nitric acid containing a few drops of hydrochloric acid, followed by 

 neutralization, gives with vitrain a clear liquid of the colour of 

 strong tea with no insoluble residue. Clarain also yields a similarly 

 coloured liquid, but contains some fine-grained insoluble residue. 



