7i8 REVIEWS 



to follow them satisfactorily. A similar statement might be made 

 regarding the methods of chemical analyses and, in later chapters, on 

 mining methods. 



It is unfortunate that with all our classifications of coal none seem to 

 meet with general approval. Probably the best is that adopted by the 

 Twelfth International Congress of Geologists, and which was originally 

 developed by D. B. Dowling of the Canadian Geological Survey. The 

 author favors a classification based upon more than two factors as best 

 meeting the requirements, but admits the inadequacy of those now in use. 



The origin of coal, through the transformation of vegetal matter 

 accumulated in swamps, is discussed in considerable detail. The amaz- 

 ing rapidity of the metamorphic processes in any such accumulation is 

 illustrated by the pebbles of coal occurring within the Coal Measures and 

 the alteration of the upper end of a mine prop which had been subjected 

 to high pressure for thirty years, during which time it also felt the effects 

 of the heat from a fire in an adjacent part of the mine. The upper part 

 of the prop and the cap wedge had a jet black color, a bright glossy 

 luster, and conchoidal fracture. Evidently the intensity of the other 

 factors may compensate for the lack of a large portion of the time ele- 

 ment usually regarded as essential in the formation of the higher grades 

 of coal. 



A chapter is devoted to the vegetation of the coal periods and deals 

 chiefly with the extinct forms. The author then takes up the structural 

 conditions existing in coal seams, the location and determination of 

 thickness of beds, and the value of coal lands. The latest mining methods 

 and the preparation of the coal and coal products for the market are 

 given due consideration. Finally a summary of the geology of the coal 

 fields and the coal resources of the world completes the volume. 



The book is adequately illustrated by well-chosen cuts, maps, and 

 photographs. The plan of the text is admirable and the author handles 

 his subject with good clear English, which is free from useless repetition. 

 This has made it possible for him to get a remarkable amount of informa- 

 tion into a single volume. Considering its size and scope, it is certainly 



one of the best texts on coal that has been published. 



C. R. S. 



Structure in Paleozoic Bituminous Coals. By Reinhardt Thiessen, 

 United States Bureau of Mines, Bulletin 117, Washington, 1920. 

 Pp. xiii+296. Pis. CLX. 

 An extensive historical review of previous studies of woody structure 



in coal is followed by a detailed description of the technique of the 



