234 



NATURE 



[February -23, 1922 



fications are based. The recently issued first Annual 

 Report of the Geological Department of the 

 Uganda Protectorate prepares us for future keen 

 discussion on several points in the proposed classi- 

 fications. Some notes on prehistoric man and on 

 caves, water supply and soils, at the end of part 2, 

 with further information in the appendices, are of 

 general interest. The numerous geological sketch- 

 maps and sections in the text, though effective in a 

 broad way, are roughly drawn and poorly printed, 

 so that the deciphering of their detail is often 

 troublesome. Though unavoidable, the big ex- 

 aggeration of the vertical scale in all the sections, 

 with the consequent severe distortion of the slopes, 

 should be constantly borne in mind, since it may 

 profoundly affect the interpretation of the struc- 

 tures, particularly where questions of faulting are 

 concerned. 



In part 3 our present knowledge of the strati- 

 graphy of the neighbouring countries of East 

 Africa and of other regions supposed to be linked 

 up with the " Great Rift " is usefully summarised 

 in short chapters dealing successively with Uganda 

 and the lakes, Tanganyika Territory, Nyasaland, 

 Madagascar, Somaliland, and Abyssinia, with some 

 reference also to the Nile Valley and Red Sea and 

 to the Palestine trough, A full bibliography, 

 thirty pages in length, forming one of the appen- 

 dices, adds to the value of the volume as a book 

 of reference. 



The book is embellished by some excellent repro- 

 ductions of scenic photographs as plates. The dia- 

 grammatic folding-maps are adapted from those in 

 the author's paper on African rift valleys in the 

 Geographical Journal (July, 1920), and have no 

 geological detail. 



With respect to the main theme. Prof. Gregory 

 has presented in his final chapter a lucid and con- 

 cise retrospect of his opinions. He still holds that 

 a great rift valley, stretching for more than one- 

 sixth of the circumference of the earth, was formed 

 by the subsidence of strips of the earth's crust 

 between parallel tension-faults, consequent upon the 

 breakdown of a precedent broad arch of elevation. 

 He believes that this structure can be traced in the 

 features of the present surface all but continuously 

 from Palestine, by way of the Red Sea and Abys- 

 sinia, across East Central Africa, southward to the 

 south-east coast beyond the Zambezi ; with branches, 

 eastward into the GuJf of Aden, and westward, by 

 way of the Central Lakes, into the Upper Nile 

 valley. The production of the " Great Rift " is 

 assigned to movements affecting the entire earth 

 between Upper Cretaceous and Pliocene times, and 

 the whole story of these movements is outlined. 



It may be so. Anyhow, the idea has its value 

 NO. 2730, VOL. 109] 



as a clear-cut working hypothesis. But we really 

 do not know much that is definite yet about the 

 structural features on which the hypothesis rests ; 

 and as closer investigation is now in progress at 

 many points along the supposed course of the 

 ' ' Rift, ' ' we may expect soon to have better grounds 

 for judgment. Already the existence of the " Rift " 

 along the Red Sea has been called in question by 

 the officers of the Egyptian Geological Survey ; and 

 in Uganda the features of the " Western Rift "are 

 pronounced by their latest investigator to be indica- 

 tive of movements of compression and not of ten- 

 sion (Geo graph. Journ., November, 192 1). It is. 

 generally agreed that the deep troughs of Central 

 and East Central Africa are due to tectonic move- 

 ment, with which severe faulting is associated ; but 

 it remains to be seen whether the troughs can be 

 strung together into a continuous chain of the length 

 and character assumed on the " Great Rift " hypo- 

 thesis. Meantime let it be acknowledged that in this 

 volume Prof. Gregory once more proves himself to 

 be the capable champion of a bold conception which 

 has already served, and will further serve, for 

 fertile controversy and the increase of earth -know- 

 ledge. G. W. L. 



The Quantum Theory. 



Die Quantentheorie : Ihr Ursprung und ihre Ent- 

 wicklung. By Fritz Reiche. Pp. vi4-23i. 

 (Berlin : Julius Spring-er, 1921.) 34 marks. 



THIS is an admirable account of the whole 

 field of the quantum theory, and should be 

 very useful to anyone who has not followed it from 

 its origin. In a subject like this, which is not yet 

 organised into a consistent whole, it is often ex- 

 ceedingly difficult to judge the importance of 

 any particular branch of the theory. One reads a 

 paper, but cannot form an estimate of its real 

 value, because there is not at hand all the in- 

 formation on cognate subjects. This is especially 

 true of the quantum theory, for the literature is 

 very predominantly German, and it is customary 

 in Germany to permit the publication of much more 

 speculative ideas than is usual in other countries, 

 and the result is that the truth tends to get lost 

 in the mass of paper. The great merit of the 

 present book is that it brings together all the 

 threads of the argument and criticises them, so 

 that a just view can be obtained of the whole 

 theory without struggling through a vast quantity 

 of literature of which a good deal is of little value. 

 It is not a mere compilation of all the views which 

 all writers have held at all times, but a critical 

 estimate of the opinions at present generally 

 accepted. 



