Reviews — The Origin of Lake Tanganyika. 419 



geological. Although the work is that of a zoologist, it thus 

 presents many features of great interest to readers of this Magazine. 

 In attempting to study it, they will only regret that, while the 

 author recognizes and discusses the geological bearings of the 

 subject, he displays such a lack of acquaintance with the elementary 

 principles of the science that the result is not so satisfactory as could 

 be wished. 



By way of introduction, Mr. Moore devotes a chapter to the 

 origin of fresh-water faunas in general, and considers that the 

 more widely-spread members of these faunas were all derived from 

 the sea at one time — " at a period roughly corresponding to the 

 commencement of the formation of the Secondary rocks." He 

 thinks that increasing salinity of the sea- water caused this migration. 

 The more sti'ictly local fresh-water types are regarded as being of 

 comparatively recent origin. 



The special case of Tanganyika is then discussed, firstly from the 

 geological and geographical point of view, and secondly from the 

 zoological standpoint. No new geological facts of importance are 

 recorded, but an interesting summary of the work of previous 

 observers is given. The peculiar ' graben ' or ' rift- valleys,' so 

 characteristic of the Tanganyika region, are unnecessarily renamed 

 * eurycolpic folds.' The Permo-Carboniferous rocks discovered by 

 the late Professor Drummond on the shores of Lake Tanganyika are 

 also misimderstood, and assumed to be marine sediments. In fact, 

 there is at present no foundation for Mr. Moore's statement " that at 

 some time there was in this region a fauna consisting at any rate 

 of ganoid fishes, echinoderms, and molluscs, or, in other words, 

 a marine fauna ; and that these things entirely disappeared through 

 the great physical changes and displacement which occurred during 

 the extension of the Nyassa fold into this particular area." If truly 

 marine deposits exist in the region in question they still remain to 

 be discovered. 



The most important zoological result of Mr. Moore's researches is, 

 that although he made large collections he never found the supposed 

 marine shells and medusEe in any lake except Tanganyika, while he 

 did not discover any striking new types, except possibly a Polyzoan 

 which has not yet been fully investigated. This circumstance is 

 ^11 the more remarkable since Mr. Moore obtained nearly 200 new 

 species of animals referable to the typical modern fresh-water fauna 

 of Africa. The fishes, described by Mr. Boulenger, and beautifully 

 illustrated, are especially noteworthy, for they are all essentially 

 present-day types, and do not in any way represent survivors from 

 the seas of the Secoudai'y period. 



The precise affinities of the medusa^ are still to be determined, but 

 Mr. Moore has examined the anatomy of the univalve molluscs in 

 great detail and with remarkable skill. He concludes that the 

 characters of the shell afford a very slight clue to the true relation- 

 ships of the animal to which it belongs. We can thus place little 

 reliance on his interesting comparison of the univalves of Lake 

 Tanganyika with certain shells of similar shape and ornamentation 

 from the Jurassic rocks -of England. His beautiful illustrations, 



