August 5, 1922] 



NA TURE 



175 



of movement " round the middle," Aristotle has just 

 mentioned (293 a 28 ff.) an argument for it which we 

 know, on the authority of Theophrastus, to be Platonic. 

 It follows, therefore, that Plato is included among the 

 " many others " who seem to agree with the Pytha- 

 goreans in denying that the earth is " at the middle," 

 and that Aristotle was well aware that the theories 

 Plato ascribes to Timaeus are not necessarily Plato's 

 own theories, as has erroneously been assumed by 

 almost all expositors of Platonism. A. E. T. 



A Rock-Desert. 



Ministry oj Finance, Egypt. Petroleum Research. 

 Bulletin No. 10. Topography and Geology of Northern 

 Sinai. Part 6, Session 1919-1920. By F. W. Moon 

 and H. Sadek. Pp. vii + 154 + 51 plates. (Cairo: 

 Government Publications Office, 1921.) P.T. 50. 



IT is no disparagement to the scientific observations 

 recorded in this volume if we notice its hand- 

 some mode of production at the outset. In printing, 

 illustration, and the inclusion of coloured sections, it 

 will bear comparison with the work of any Geological 

 Survey in the world. Two coloured maps on the scale 

 of 1 : 250,000 are folded in a pocket at the end, and these 

 are mounted on linen, a feature almost unique in 

 official publication. 



The researches that are placed in this permanent 

 form before the public could not have been undertaken 

 by private enterprise. Their object is to furnish a 

 basis on which exploration may go forward in search of 

 petroleum in Sinai, guided by the stratigraphy of a 

 difficult and arid region. The oil-indications occur in 

 Upper Cretaceous strata, mainly in the Cenomanian 

 series, and any local concentration that may be found 

 will depend on these beds as the primary sources 

 of supply. Two places where the conditions seem 

 favourable have been recommended to the Egyptian 

 Government as sites for boring (p. 142). The clean 

 I exposures of rock-edges allow the geologist to read the 

 structure of this desert country, as he can among the 

 I splendid folds of the Lange Bergen or in the high 

 I plateaus of Arizona. The features of a rock-desert are 

 admirably pictured in photograph No. 12, where some- 

 thing is seen of the most notable structural feature of 

 the region, the Cretaceous beds being strongly folded 

 as they are traced downwards, while the conform- 

 able Eocene above them is almost undisturbed. The 

 dome-structure sought for by oil-prospectors is thus 

 present in the areas where beds older than the Santonian 

 are exposed, but is scarcely to be traced in higher series. 

 The authors, after a useful historical review (p. 37), 

 advise the abandonment of the term Nubian Sandstone 

 as indicating a stratigraphical horizon. 

 NO. 2753, VOL. I 10] 



A thin band of potassium salt has been found under 

 Gebel Sinn Bisher, a place where old workings, prob- 

 ably for rock-salt, may be traced. We may note the 

 spelling Gebel, for Jebel, now adopted in Egyptian 

 memoirs, which will commend itself equally to English- 

 speaking folk. We congratulate Messrs. Moon and 

 Sadek on carrying out this fine piece of mapping in a 

 country where " life is, at its best, a very hard one," 

 and where the Arab natives speak, quite happily, of 

 their " homes " in caves cut in the mountain sides. 



G. A. J. C. 



Our Bookshelf. 



La Geographie de I'Histoire : Geographie de la Paix et de 

 la Guerre sur Terre et sar Mer. Par Jean Brunhes 

 et Camille Vallaux. Pp. vi + 716. (Paris: Felix 

 Alcan, 1921.) 40 frs. net. 

 Two distinguished French geographers have collabor- 

 ated in producing a volume on the relations of geography 

 and history, which is really a treatise on political 

 geography. Rather more than half the volume is 

 concerned with the principles of the subject, and the 

 remainder with their application to current political 

 and social problems, arising out of the redistribution 

 of territory and alterations in frontiers after the war. 



Beginning with the thesis that man is the chief geo- 

 graphical agent, since he can more effectively modify 

 the surface of the earth than the physical agencies at 

 work, the authors consider the distribution of man. 

 Regions of dense population may be either zones of 

 passive concentration where conditions favour increase 

 in numbers but do not demand any great degree of effort 

 in order to find nutriment, and zones of active concen- 

 tration where man, reacting against conditions not 

 wholly favourable, triumphs by the exercise of effort. 

 In the first category are regions of high temperature 

 with considerable atmospheric humidity and abundant 

 surface water, like the Chinese river valleys or the 

 Nile delta. In the second category are oceanic border- 

 lands and islands in temperate regions where conditions 

 entail some struggle against sea and climate but are 

 not unpropitious. In this category also are the areas 

 where temperate forest has to be cleared and where 

 coalfields are exploited. 



From these " facts of fixation " the authors pass to 

 " facts of movement " and discuss the influences behind 

 migration and human movements. Some of the most 

 important chapters in the book are those which deal 

 with the growth and stability of states and the positions 

 favourable to sites of capital cities. In struggle, though 

 not necessarily war, the authors see one of the essentials 

 for the healthy life of a state. Struggle means growth, 

 but a state of political and social equilibrium means 

 stagnation and decay. We have no space to do justice 

 to this volume, and have indicated only a few of the ideas 

 it contains. Every step in the authors' arguments 

 is abundantly illustrated by concrete examples. The 

 only drawback to the book is its lack of lucidity in 

 places. The style at times is more ponderous than 

 one would expect from French writers. There are 

 black and white maps and full indices. 



