484 SCIENCE PROGRESS 



A Manual of Seismology. By Charles Davison, Sc.D. [Pp. xii + 246, 

 with 100 figures.] (Cambridge: at the University Press, 192 1. Price 

 21S. net.) 



The subject of seismology is of comparatively modern growth, and borders 

 on many branches of science. A knowledge of the essential facts of the 

 subject is necessary alike to the geologist, the geodesist, and the physicist. 

 Dr. Davison has performed a useful service in collecting together these facts 

 into a connected form in the volume under review, which may serve both as 

 a textbook for the student and as a reference volume for the investigator 

 requiring information on any particular point. For this purpose, the com- 

 prehensive references to original papers will prove of great value. In general, 

 at the beginning of each chapter is given a list of the more important memoirs 

 dealing with the branch of the subject under consideration, whilst detailed 

 references required in each section are collected in a footnote at the end of 

 the section. 



The volume forms one of the Cambridge Geological Series, and it is, 

 therefore, natural that particular attention is given to the geological side of 

 the subject. It is perhaps to be regretted that, for the sake of completeness, 

 more space was not devoted to the recent physical developments, connected 

 with the propagation of seismic waves and the information to be derived 

 from earthquakes as to the physics of the earth's interior, although other 

 works are available which deal in detail with these branches. 



A real need is met, and well met, by the publication of this work. 



H. S. J. 



Oil-Finding : An Introduction to the Geological Study of Petroleum. By 



E. H. Cunningham Craig, B.A., F.R.S.E., F.G.S. Second Edition. 

 [Pp. xi + 324, with 13 plates and 20 text-figures,] (London : Edward 

 Arnold, 1920. Price i6s. net.) 



A COMPARISON of the second edition of this book with the first one shows 

 that, while the arrangement is substantially the same, the volume has under- 

 gone considerable revision and has been much enlarged. In the earlier 

 chapters on the origin of petroleum, the inorganic theories, however, still 

 receive scant treatment, while the exponents of the " animal origin " are 

 informed, at some length, of the utter failure of their theory when tested in the 

 field. For the author, the " vegetable origin " is the theory most in accord 

 with the facts ; he holds most strongly the opinion that the mineral oil is 

 derived from the decay of vegetable matter and owes its local concentration 

 to the influence of geological structure. The importance of the theory of 

 origin is urged so strongly by the author that it is all the more unfortunate 

 that his treatment of the subject is polemical. In a book of this kind, it 

 would probably have been better if the inorganic theories had not been dis- 

 missed in such a cavalier fashion and the " vegetable origin " discussed from 

 a less antagonistic point of view. The whole subject is so far removed from 

 any state of finality and the theories so far in advance of practical verification 

 that it is doubtful whether a hard-and-fast adherence to any one mode of 

 origin for all the diverse occurrences is wise. 



Among the new chapters which have been added is one on natural gas 

 and another on oil-shales and torbanites. In the former, comment is made 

 on the general lack of recognition of the importance of gaseous petroleum, and 

 the author points out that, in North America, " the value of the gaseous 

 petroleum won and utilised in a year is far in excess of that of the oil." It 

 is also interesting to note that, while the author is sceptical of the possibility 

 of workable quantities of oil in great Britain, he is more hopeful about the 

 occurrence of natural gas. In the latter chapter, emphasis is laid on the 

 different nature of the " yellow bodies," which are the source of the oil in 



