August 19, 1922] 



NA TURE 



243 



permeable rocks does not appeal. His conclusions as 

 a follower of water by sheer hard climbing and ex- 

 ploration underground are supported by the very 

 varied results of borings made near one another in 

 beds regarded as porous by the engineer. M. Martel 

 believes, with much justice, that subterranean rivers 

 do not etch out their own way ; they are determined 

 by pre-existing crevices, the diaclases of Daubree. 

 In the case of limestone, solution obviously widens 

 the original fissure ; but it must have been generally 

 recognised that the long-continued dominance of the 



I joint-system is again and again revealed in the plans 

 of sinuous caves. 



M. Martel, however, does not give geologists much 



! credit for observing a relation between the direction 

 of surface-streams and the fissured structure of a 

 country ; but we cannot help remembering the account 

 of the Drava and Gail system in the first volume of 

 Suess's " Antlitz der Erde," and the exposition by 

 Molyneux and Lamplugh of the Batoka Gorge of 



I the Zambezi. In the case of Mosi-oa-tunya, however, 

 M. Martel seems satisfied with the somewhat cata- 

 strophic views of Livingstone. We must admit that 

 an examination of our ordinary text-books reveals 

 an unfortunate silence on this question of fissures 

 and stream-erosion ; but surely M. Martel is inclined 

 to exaggerate (p. 42) the differences between his views 

 and those of colleagues like Lugeon, Kilian, and de 

 Martonne. He is accustomed to move adventurously 

 in narrow rift-like ways, along the floors of ravines 

 and their counterparts underground ; but he cannot 

 wish us to return to the antique view of valleys as 

 gaping fissures in the crust. On a tilted peneplain 

 the courses of streams are at first uncertain ; they 

 are controlled merely by the general slope. When they 

 have worked down into the surface of solid rock, they 

 at once begin to be guided by the joints, the lines of 

 weakness. The walls of the ultimate valleys are due 

 to erosion ; the general ground-plan is often deter- 

 mined by that of the joints, the walls of which are 

 practically in contact until the streams begin to work. 

 The surface-waters then cut downwards. By 

 seepage they become subterranean, and the diaclases 

 prove still more effective in the underworld. The 

 details of caves and of disappearing and reappearing 

 streams are never monotonous to M. Martel ; but the 

 frequent photographic representation of them may 

 pall a little on the geological or engineering reader. 

 We must admit that the pictures here given, to the 

 number of three hundred, are fascinating and often 

 very impressive. In some cases, as in those of the 

 canon of Olhadibie in the Basses-Pyrenees, they result 

 from very recent exploration. 

 The discussion of the origin of water in the Chalk 

 NO. 2755, VOL. I 10] 



(p. 366) raises important engineering considerations. 

 Mr. R. L. Cole has recently dealt with this matter as 

 regards the south of England (" The Power User," 

 June 1922, p. 97), and he treats the body of the Chalk 

 as providing little opportunity for flow. M. Martel, 

 in his descriptions of " lapiaz " or " lapies " (p. 531), 

 shows well how water penetrates a limestone surface 

 and how it proceeds to ramify below. His remarks 

 on the use of the divining-rod (p. 749) are philosophic 

 and reserved ; he looks for a very extended series of 

 trials made on a consistent plan. The power of divina- 

 tion, if it exists, resides in the operator and not in the 

 instrument used. He shows, among other interesting 

 matters, how the sinking of artesian wells was known 

 to dwellers on the edge of the Sahara centuries before 

 Moorish engineers were invited to find water in Artois. 

 The ease with which subterranean water may be 

 contaminated is attested by grim instances (p. 767) 

 of the slow decomposition of corpses interred on the 

 battlefields of 1914-18, and by the infection during a 

 whole year of the spring of Gerbeviller in Lorraine. 

 Grenville A. J. Cole. 



Statics, Dynamics, and Hydrodynamics. 



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