August 13, 1896] 



NA TURE 



549 



It may, however, be doubted whether this theory, which 

 its author terms that of plateau eruption, is really different 

 from the explanation of the so-called fissure eruptions 

 jiiven in Sir A. Geikie's text-book. 



It is when we pass from the purely geological chapters 

 to those portions of the work that refer to the East 

 African fauna and tlora, and to the descriptions of the 

 various tribes who inhabit the country, that we come to 

 what will probably prove to many readers the most 

 attractive portion of Dr. Gregory's 

 work. The pages relating to the 

 present and past distribution of life 

 teem with original suggestions, and 

 many of the observations made on 

 the journey are highly novel and 

 interesting. Amongst these are some 

 curiotis cases of mimicry, especially 

 that represented in the frontispiece 

 to the volume, in which a group of 

 hemipterous insects, red and green, 

 presents an astonishing similarity 

 to a flower-spike. Remarkable ex- 

 amples are given of the disappear- 

 ance of wild animals, such as buffa- 

 loes and giraffes, throughout a very 

 Jarge tract of country, in consequence 

 of disease ; whilst observed instances 

 of the destruction of great numbers 

 by drought, and the accumulation of 

 their skeletons around isolated water- 

 holes, are suggested as perhaps ar 

 counting for some of the enormoii- 

 inasses of mammalian bones thatai< 

 found imbedded in particular strata. 

 Jt is not necessary to agree with 

 suggestions of this kind in order to 

 recognise their \'alue ; and unc|ues- 

 tionably under the conditions pointed 

 out, if the bones are, soon after the 

 death of the animal, enclosed in silt 

 or gravel, they may be preserved. 

 Hones exposed on the surface, how- 

 ever, especially in the tropics, deca\ 

 and break up with great rapidity, 

 and the accumulations of fossil bone> 

 occasionally found are more probably 

 due to carcases, carried down by :i 

 river flood, having collected in 

 backwater or on a sandbank. 



One example of a suggestion i 

 the author's, peculiarly illustrative "i 

 his double range of investigation, ;i- 

 geologist and as biologist, may hcrr 

 be noticed. It has long been know n 

 — we are indebted to Dr. Ciuntln 

 for the original facts — that the fre-1 

 water fish-fauna of the Jordan an 

 Sea of Galilee resembles in cert.n 

 peculiarities, such as the presence ul 

 the genus Hemicliromis, that of the 

 Central African lakes more than that 

 of Northern Africa and of the lower 

 Nile basin. Dr. Gregory shows the 

 possibility of the Red Sea depression 

 having once been the valley of a ri\ er 

 flowing into the Indian Ocean, and receiving near 

 its mouth a tributary from the large lakes that formerly 

 existed in the Rift X'alley, and that may have occupied 

 a considerable portion of what is now the upper Nile 

 basin. This is of course, as is fully admitted, hypothesis, 

 but it is supported by a very curious mass of data, and it 

 explains the difficulties better than any other suggestion 

 hitherto put forward. 



One characteristic of Dr. Gregory is a taste for namin;,' 

 i\0. 1398, VOL. 54] 



various things, past and present. In many cases this is 

 useful, as when he maps and names the ridges and valleys 

 of Mount Kenya. It may also be of service to have a 

 name, like Lake Suess, for an ancient sheet of water of 

 which evident traces remain ; but it is somewhat question- 

 able whether there is any advantage in calling the 

 hypothetical stream, that may at some past time have 

 traversed the Red Sea, the Erythriean river. In one 

 case the author of the " tireat Rift Valley" appears, in 



the application ot names, to have departed from 

 the usual practice. Geologists have generally given 

 local names to rock-systems and their divisions, and 

 have referred them, so far as they were able, to 

 the geological periods, or divisions of geological 

 time, recognised in Europe. To judge by the table 

 at p. 235, certain names — Naivashan, Laikipian, &c. 

 — are given to divisions of geological time rather 

 than to rock-masses, and it is fairly open to gra\e 



