668 . SCIENCE PROGRESS 



in Great Britain," the sentence " coal forms a distinct layer or bed varying 

 from a few inches to as much as 300 feet in thickness" is not annotated to 

 explain to the presumably ignorant student that no coal in Britain approaches 

 anytliing like 300 feet in thickness. 



Occasionally the name of someone distinguished in coal research is 

 mentioned, but never with any reference to indicate to a reader where to find 

 his work. As a rule, names which were famous half a century ago rather 

 than those of any recent workers are cited. For instance, in Chapter III, 

 the old (and one thought now quite defunct) controversy over in situ 

 and " drift " origin of coal is rehashed, and the statement which hardly 

 anyone of authority or experience would agree with is made that, " In 

 this country .... due mainly to the teaching of Logan, de la Beche, and 

 Principal Dawson, a coal-seam is considered to represent an original peat- 

 bog." Dawson, who was most active in the sixties of last century, should, at 

 least, have had coupled with his name some palaeobotanist who has done 

 more recent research. 



It seems a pity to rattle old bones over this so foolish controversy, but if 

 it must be disinterred (one thought even its ghost was laid by the clear 

 and simple fact that some seams were grown in situ and the accumulations 

 forming others were drifted) the arguments used on either side should be 

 expressed precisely or the student will be left in a fog. 



Such a sentence as that " the condensed vegetable pulp quickly hardened 

 or passed into coal ... is shown by the not infrequent occurrence of angular 

 or rounded pebbles of coal embedded in the coal-measure sandstones of most 

 coal-fields " occurs on page 25. What is the student, uninstructed save by 

 this book, and not referred to more precise authority, to assume is meant 

 by the word " quickly " — a season ? a decade ? a century ? a hundred 

 thousand or a million years ? In relation to the vast extent of the coal 

 measure deposits half a million years might very well elapse between the 

 formation of one accumulation and its break-up to form actual pebbles for 

 the higher measures. While, of course, no one can say what periods of time 

 are represented between such beds, still the teacher should offer some guide 

 to the student regarding the possible limits of the meaning of the word 

 " quickly " used in such context. 



Looseness of thought degenerates into absolute inaccuracy in the sentence : 

 " The increase in weight due to the conversion of wood into coal, etc." 

 During the conversion of wood into coal by the various organic processes 

 which took place, wood actually lost gaseous vapour and portions of its 

 organic molecules ; hence there can be no increase in weight when wood is 

 converted into coal, but, on the contrary, a very material decrease in weight. 

 Owing to the pressure on the mass, there is an increase in specific gravity ; 

 but the accurate discrimination between " weight " and " specific gravity " 

 is a lesson for elementary school-children, and mining students should not 

 be involved in their confusion. 



After these criticisms we must close with a few words of appreciation 

 of the chapter dealing with the practical prospecting and boring, which is 

 quite useful, and of the later part of the book in which the clear maps and 

 diagrams and the correlation of the various seams will be useful to many. 



BOTANY 



General Botany for Universities and Colleges. By Prof. H. D. Densmore, 

 M.A. [Pp. xii + 459, with 289 illustrations.] (London and New 

 York : Ginn & Co., 1920. Price 125. 6d. net.) 



As in most textbooks on Botany that have recently appeared, the author 

 has adopted a functional treatment of structure. Starting with the relation 

 of plants to their environment, the student is led to consider their structure 



I 



