5i8 



NATURE 



[January 15, 1920 



trie scheme for the Dominion. Mr. E. Parry's great 

 North Island scheme should be put in hand at once, 

 including the electrification of the East Coast railway. 

 The people in the South Island also should insist on a 

 national scheme. 



Dr. .\dams, in addition to his papers already 

 noted, read others on (i) "Determination of the Posi- 

 tion of the Moon by Photography," illustrated by 

 photographs from the Lick Observatory. The very fine 

 star images secured indicate the high efficiency of the 

 Crossley reflector telescope, which was driven without 

 any guiding, and the photographs prove that the posi- 

 tion of the moon and terrestrial longitude can be 

 determined with high precision. (2) "The .Mniucantar 

 Method for Determination of Time and Latitude." 

 (3) "A Nomogram for Transit Instrument Star Fac- 

 tors." Dr. Adams exhibited also some photographs 

 on glass of the solar corona received by the Hector 

 Observatory from Dr. W. W. Campbell, of the Lick 

 Observatory in California. The photographs were 

 taken by the Crocker Eclipse Expedition on June 8, 

 1918, at the total eclipse of the sun, with a 40-ft. 

 camera pointed directly at the sun, and using 10 in. 

 by 12 in. plates. The Lick Observatory' had most 

 remarkably good fortune at this eclipse : the sky had 

 been completely cloudy all day, but cleared up in the 

 neighbourhood of the sun one minute before totality, 

 and this small portion of the sky remained clear until 

 a few seconds after totality. The small region of un- 

 clouded sky containing the totally eclipsed sun seemed 

 to be quite clear and was the bluest sky seen by the 

 expedition. 



Section 4, General, had papers on "Moriori Art," by 

 Mr. H. D. Skinner, lecturer on ethnology at Otago 

 University; "The Language of the Chatham Islands," 

 bv .'Vrchdeacon H. W. Williams; and "The Natural 

 Laws of Poetry," by Mr. J. C. .Andersen. The following 

 papers, read in the General Section, should more pro- 

 perly have been included in Section i, viz. "Afforesta- 

 tion in New Zealand," by Mr. W. H. Skinner; "Some 

 Proposals with regard to Natural Afforestation in a 

 New Zealand Mountain Area," by Mr. W. G. Morri- 

 son; and "Preservation of New Zealand Fauna," by 

 Mr. E. G. Stead. 



THE AFRICAN RIFT VALLEYA 



AFTER the discovery of Lake Rudolf in 1888, Suess 

 showed that the Jordan, Dead Sea, and Red Sea 

 fractures were not continued along the coast of Africa, 

 but through the East .African lake chain, the basins 

 of which had been formed by the foundering of their 

 floors between parallel faults. During an expedition 

 to British East .Africa in 1892-0)3 Prof. Gregory con- 

 firmed Suess's conclusions, with some modifications 

 as to the age and origin of the Great Rift Valley, the 

 formation of which he attributed to successive faulting 

 during the great earth movements of the Kainozoic 

 era. 



The Rift Valley has been traced from northern 

 Palestine to southern Africa. Its structure varies with 

 its age an3 the nature of the country traversed. Thus 

 the fault-scarps are better preserved along the Gulf of 

 .Akabah than in the older sections which enclose the 

 Red Sea and the Gulf of Suez. The section in 

 southern Abyssinia which connects the Red .Sea with 

 Lake Rudolf and the Rift Vallev in British East 

 .Africa is locally irregular where intersected by the 

 cross fractures that bound the sunk land of the Gulf 

 -of .Aden. Across British East Africa the valley is a 



1 From a paper read before the Royal Ge >graphical Society on January 5 

 by Prof. J. W. Greeory, F.R.S. 



NO. 2620, VOL. 104] 



comparatively simple trench ; its walls are often so 

 steep that Sir John Bland-Sutton describes them as "as 

 steep and abrupt as those of a grave," and for long 

 the Uganda Railway worked its trains between the 

 valley and plateau by a rope incline, and there is still 

 no road for wheeled traffic from Nairobi to the floor 

 of the Rift Valley. 



South of British East Africa it has been claimed 

 that the Rift Valley comes to an end, only its western 

 wall being continued as a fault-scarp. This arrange- 

 ment occurs near Lake MSnyara, where the eastern 

 side is a long, smooth slope which ends westward at 

 the fooj of the fault-scarp that bounds the Giant 

 Cauldron Mountains. The structure mav be explained 

 as an extreme case of the asymmetry due to the 

 different strengths of the rocks on the two walls. In 

 southern British East .Africa at Lage Magadi the 

 western wall is a high, steep scarp, while the eastern 

 side consists of a number of wide, flat steps due to 

 parallel faults. At Lake Manyara, as the rocks on 

 the eastern side are softer, the scarp has been dressed 

 down to an even slope. This arrangement does not 

 extend far ; the eastern wall soon reappears, and, 

 though Suess left a gap of 350 miles long between 

 Lakes Manyara and Nyasa, the Rift Vallev has now 

 been traced across most of it. 



That Nyasa is a Rift Valley basin has been proved 

 by Andrews and Bailey. Its northern end is joined 

 bv the western branch, which includes Tanganyika, 

 the .Albert Nyanza, and the Upper White Nile. In 

 the western branch the valley is in places irregular. 

 as branches run off or the course is deflected along 

 the grain of the country, to which that branch as a 

 whole is oblique. South of the Zambezi the Rift 

 Valley has been traced by Teale and Wilson, who have 

 shown that a post-Eocene rift valley separates the 

 Sheringoma plateau from the eastern front of 

 Rhodesia. The long meridional section of the cosst 

 from Beira to Cape Corrientes appears to have bei;n 

 determined by the southernmost of the crustal move- 

 ments of the Great Rift Valley. 



The vallev, therefore, extends from Lebanon to the 

 Sabi River; its branches reach the mouth of the Gvlf 

 of .Aden, and westward include the rift valleys of the 

 Eastern Congo. Its length is about one-sixth of the 

 circumference of the earth; hence it must have had 

 some world-wide cause, the first clue to which is its 

 age. The view that its history is geologically short 

 commends itself by the freshness of its walls, by the 

 legends of catastrophes, such as the destruction of 

 Sodom and Gomorrah and the drowning of many 

 villages on the formation of Tanganyika, having 

 occurred along it during the time of man, and also 

 bv the fact that many of its faults are certainly recent. 

 Nevertheless, the fuller evidence now available con- 

 firms the classification advanced in i8q6, which attri- 

 buted some of its lavas to the time of Chalk, and 

 represented some of its faults as older than the uplift 

 of the Alps. Some beds attributed to the Miocene 

 on phvsiographical evidence are now proved of that 

 date bv the evidence of fossils. The rift vallev of the 

 Red Sea was certainly in existence by the Oligocene, 

 and the southern end of the valley is shown to be of 

 the same date bv a fossil sea-urchin which has now 

 been proved to be an East .African species. 



The history of the Rift Valley is largely dependent 

 on the volcanic history of the country traversed. Tho 

 first step in its formation was the uplift of a bronrl 

 band of highlands extending from Palestine to Natal. 

 The weakening of the support led to the collapse of 

 the summit of this ridge. The sinking of the key- 

 stone caused volcanic eruptions along the adiacent 

 fractures. The earliest of the great eruptions probably 



