ESSAY-REVIEWS 75 



The Americans are particularly fortunate in having in 

 their country not only extensive coal-basins of Carboniferous 

 age, but also coals of Mesozoic and Tertiary ages ; so that their 

 outlook on the whole subject of coal formation should be 

 much better balanced than that of those whose data are 

 restricted. The value of this wider experience should be 

 particularly evident in connection with that interesting puzzle — 

 the cause of the anthracitisation of coals. The old-fashioned 

 idea that anthracites are essentially palaeozoic is, of course, 

 immediately demolished by a study of the Cretaceous and 

 other Anthracites in America and Asia ; and so one very much 

 wishes that the sections of White and Thiessen's paper touching 

 on the subject were much fuller and more detailed than they 

 are. One theme which is brought out clearly by these authors, 

 is, to quote the words of their short conclusion, " The degree of 

 decomposition, elimination, maceration, chemical reduction, 

 and constitution, in any one stage [of coal- formation] depends 

 on the species, kinds of parts, organs and products contributing 

 to the deposit originally ; the efficiency and duration of action, 

 chiefly of the biochemical agencies, during the peat stages ; 

 and the efficiency and duration of action of the dynamochemical 

 agencies during the coal stages." 



The plates show many interesting structures in coal sections ; 

 but suggestive and exhaustive in some respects though the work 

 be, it leaves one continually asking for more data, more details, 

 more illustration. The fact that over three hundred pages 

 and fifty plates leave one feeling that the whole subject is 

 merely indicated rather than presented completely, shows the 

 extent of the problems involved. 



The paper on the South Wales coalfield is a great contrast 

 to the American work. Those themes on which it enters it 

 deals with more exhaustively, and there are many pages of 

 details and analyses which will be invaluable to specialists. 

 The interpretation of the true meaning of the chemical analyses 

 of coals is a very difficult subject, which is well handled with 

 many useful figures, in this paper. The detailed charts of the 

 distribution of the anthracitic zones, prepared with such care, 

 bring out clearly the relative positions of the anthracitic and 

 bituminous portions of the seams, and must be of service not 

 only to science, but to practical miners. These charts illustrate 

 strikingly the fact that the isoanthracitic lines congregate 



