54S 



NA TURE 



[August 13, 1856 



seven chapters and three appendices, affords a jfeneral 

 summary of the scientific results. 



The "Great Kift X'alley," of which tlie characters were 

 first indicated by Sucss, is a fissure in the earth's surface 

 into which, or into portions of which, a strip of the surface 

 itself has been let down by parallel faults. The clifTs 

 formed by the faults have not been removed by denuda- 

 tion, and the necessary inference is that the dislocation — 

 partially, at all events — is of small geological antiquity. 

 The great fissure itself is regarded as similar in character 

 to certain lines, resembling cracks, that have been ob- 

 served on the moon's surface : it lias been traced at 

 intervals from the valley of the Zambesi to Lake Rudolf, 

 and it is supposed to be connected through tlie trough of 

 the Red .Sea with the depression containing the Jordan 

 Valley and the Dead Sea in Palestine. From Lake Rudolf 

 a branch rift appears to diverge to the west, and to lead 



of the valley examined by him— fifty to seventy miles on 

 each side of the equator, or about 120 miles in all— is 

 actually let down by faults on each side. He has also 

 shown that great changes in elevation must have occurred 

 throughout the area in comparatively recent geological 

 tmies, and that one of these led to the formation of a 

 large lake, of which traces are left in the form of terraces 

 on some of the scarps that bound tlie Rift Valley. To 

 the ancient lake Dr. Gregory applies the name of Lake 

 Suess ; and, if a name is required, no more appropriate 

 one could be devised. 



The discoveries on Kenya were even more important 

 than those in the Rift \"alley, for not only did Dr. Gregory 

 find glaciers, but he met with clear evidence that these 

 glaciers formerly descended more than 5000 feet lower 

 down the mountain than they now do. Reasons are 

 given— one of the most important being the absence of 





U all ol l.K Kiit \ .dk-y, will, th.^ 1 I 



through Lakes Albert and Albert Edward to Tanganyika ; 

 whilst south of Lake Rudolf the eastern branch, our 

 knowledge of which has been materially increased by Dr. 

 <;regory's examination, contains several smaller lakes— 

 Baringo and Naivasha, amongst others— and probably 

 terminates to the southward in Lake Nyassa. Altogether 

 this wonderful north and south trough is regarded as 

 having a length of 4000 miles, and is said to contain 

 thirty lakes, of which only one has an outlet to the sea. 

 Evidently only the eastern branch of the rift is referred 

 to, fo : three large lakes in the western branch— the Lakes 

 Albert, Albert Edward, and Tanganyika arc drained by 

 the Nile or the Congo. 



The principal additions to our knowledge of the "Great 

 Rift Valley" are two in number. Dr. Gregory has shown, 

 apparently beyond any chance of error, that the portion 

 NO. 1398, VOL. 54] 



any similar evidence on Kilimanjaro — for doubting 

 whether the former extension of glacial action on Kenya 

 was due to a general refrigeration of the earth's surface 

 in the glacial epoch, and it is inferred that Kenya and 

 the surrounding area have undergone depression since 

 the period of maximum glaciation on the mountain. This 

 may be the case, but it leaves the great difficulty of the 

 whole question unexplained : we ha\e still to account for 

 the isolated occurrence of temperate plants, both of 

 northern and southern types, on all the Central African 

 mountains. 



A considerable mass of interesting details on the 

 geology of the country lying between the coast and the 

 Rift \"alley is given, and incidentally, with reference to 

 the great lava plains traversed, their origin is discussed 

 and a theory put forward to account for the phenomena. 



