NATURE 



461 



HURSDAY, SEPTEMBER 6, 1906. 



A7/,K STUDIES. 

 Till' I'livsiograffliv of the River Silc ami ils Basin. 

 Bv Captain H. (i. Lyons, Dirpcloi-Gf-noral, Survey 

 Diparlment. Pp. viii + 411; with 48 plates, 

 (("airo: National Printing- Department, 1906.) 



WiII-2\ a British army was first sent to occupy 

 l-;t,'ypl. the late Prof. Huxley called upon the 

 Royal Society to appoint a committee to arrange for 

 a systematic study of that most interesting country. 

 He justly pointed out how much the French Govern- 

 ment had accomplished in the promotion of scientific 

 research and in the publication of its results during 

 their short period of occupation at the beginning of 

 last century, and he declared that it would be a 

 national disgrace if we failed to accomplish some- 

 thing of the same kind with our much greater oppor- 

 tunities. 



The publication of the work before us, and of others 

 of a similar character, serves to show that England 

 has not been unmindful of her responsibilities or 

 neglectful of the opportunities which have resulted 

 from our close association with the Egyptian Govern- 

 ment for more than two decades. Captain Lyons, 

 who organised the Geological Survey of Egypt — some 

 of the admirable publications of which have been 

 reviewed in the pages of Nature — has now become 

 head of the whole Survey Department of Egypt, and 

 is administering its affairs with characteristic energy 

 and ability. 



The discovery of the Lake district of Equatorial 

 Africa by Speke and Grant, with the surveys and 

 observations of Gordon, Emin, Schweinfurth, Junker, 

 and others, has afforded a safe basis for the treatises 

 on Nile hydrography by Kloden, Lombardini, Cha- 

 vanne, and de Martonne ; but since the fall of Omdur- 

 man in 1898, and the consequent opening up of the 

 Sudan, much new material has been made available. 

 Systematic meteorological records have been collected 

 at various stations in L^ganda, Abvssinia, and the 

 Sudan, and careful rneasurements have been n^ade of 

 the levels, at different seasons of the year, of the 

 several lakes and of the amount of water discharged 

 by each of the Nile tributaries. .All these sources 

 of information have been admirablv utilised by 

 Capt.-iin Lyons in his survey of the present state of 

 our knowledge of Nile hydrography. 



.\fter a very interesting discussion of the climate 

 and rainfall of the districts, from which the waters 

 of the Nile are supplied. Captain Lyons proceeds to 

 describe in detail the eight regions into which the 

 Nile basin may be conveniently divided. Recent 

 surveys in most of these districts have given much 

 greater precision to our knowledge of their physio- 

 graphy, geology, meteorology, and other natural 

 features. 



The Lake Plateau, which has an average elevation 

 of about 5000 feet, is composed of various meta- 

 morphic rocks. The centra! part of the area is 

 occupied by the great Lake Victoria, while in its 

 western part is the deep rift valley with Lakes Albert 

 NO. 1923, VOL. 74] 



Edward and .Albert. Tlte district is characterised by 

 rapids and marshes, no regular flow of the streams 

 having been established by erosion, but the effective 

 supply to the Nile from the Victoria Lake varies 

 from 500 cubic metres to 1000 cubic metres per 

 second. 



The basin of the Bahr el Jebel, Bahr el Zaraf, and 

 Bahr el Ghazal, although having a very heavy rain- 

 fall, really absorbs, not only this, but a considerable 

 part of the water supplied to it from the Lake 

 Plateau. The rivers wind through level alluvial 

 plains, and support a great marsh vegetation (the 

 " sadd "), consisting of papyrus and various reeds 

 with some floating plants, and evaporation and 

 absorption by vegetation take up, not only the whole 

 of the considerable rainfall, but diminish the amount 

 coming from Lake Victoria by from 4 per cent, to 

 52 per cent. 



The Sobat Basin is occupied by a comparatively 

 short river with a rapid fall, and adds an appreciable 

 but varying amount to thi' waters coming down the 

 White Nile. 



In the White Nile Basin vv-e find that we have the 

 most constant element in the supply of the Nile 

 waters. The 1500 million cubic metres of water from 

 the Sobat flood are supplied to the Nile during October, 

 November, and December, thus modifying the fall in 

 the water-level of the river during those months. 



The Blue Nile, the Atbara, and the Khor el Gash. — 

 These rivers drain a pilateau with an elevation of 

 from 6000 feet to 10,000 feet. .Although exact in- 

 formation concerning the distribution of rainfall in 

 various parts of the .Abyssinian highlands is still 

 wanting, there can be no doubt that the rainfall is 

 very great. The regular northward movement of the 

 rain-belt during the monsoon season leads to the 

 flooding of Vne Blue Nile and Atbara, and the annual 

 Nile fiood in July, August, September, and October. 

 The volume and continuance of this flood are clearly 

 dependent, firstly, on the amount of rainfall in the 

 .Abyssinian highlands, and secondly, on the great 

 length of the river courses, with their deeply-cut 

 channels, ensuring a regulation of the water supply 

 during torrential rains. Captain Lyons directs atten- 

 tion to the possible interference w ith this latter element 

 in the production of the periodic Nile floods, which 

 may result from the extensive afforestation which is 

 said to be going on in .Abyssinia. 



From Khartoum and Berber to .\siiuan the united 

 waters of the White Nile, Blue Nile, and Atbara flow 

 in a single stream, which is eroding its bed with 

 considerable rapidity, there being some cataracts but 

 no flood plains. The waters of the Nile have in this 

 part attained their maximum, and in its course north- 

 ward the river is constantly losing by evaporation and 

 the withdrawal of its waters for irrigation. 



From .4s'zt'an to Cairo the Nile flows in a depression 

 in which it has deposited a considerable thickness of 

 alluvium, and the river winds through the flood plains 

 thus formed. During the fifty centuries of which we 

 have a record, the Nile appears to have deposited a 

 thickness of 16 feet or 17 feet of alluvium in this 

 part of its course, and the silting up of various water 



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