54 NATURAL SCIENCE. July. 



accessible to a limited number of readers ; but the author has, as a 

 rule, been successful in hitting the happy mean between brevity and 

 diffuseness. 



No fates could have seemed more adverse than those which 

 awaited Dr. Gregory on his arrival in Africa : the well-equipped expedi- 

 tion destined for Lake Rudolf went to pieces before it had advanced 

 more than a few days' journey from Mombassa, its leader apparently 

 left it to shift for itself, and Dr. Gregory's sole recompense for having 

 wasted full three months was a couple of bad attacks of fever. Most 

 men would have quitted Africa in disgust. But that is not his way, 

 so he determined to make a dash at Lake Baringo and Mount Kenya. 

 * Make a dash ' is the right term, for his party, of necessity, was small 

 and not too well provided, a belt of country over-run by the formidable 

 Masai had to be crossed, and his time was short. It was, in fact, a 

 record performance. The party, in going and returning, covered 

 1,650 miles in two days less than five months. 



It was formerly held, as Dr. Gregory remarks, that the geology 

 of Tropical Africa was exceptionally monotonous. It was a continent 

 without a history, where, in truth, there was nothing new under the 

 sun. This idea he shows to be very far from correct. No doubt the 

 palaeontological record is singularly deficient, for a large area is 

 occupied by gneisses and schists, almost certainly representative of the 

 Archaean era ; another area, by no means small, is covered with great 

 sheets of lava. There are, however, some stratified rocks ; and the 

 geological record becomes more complete towards the end of the 

 Secondary era, though the explorer is seldom tempted to overload his 

 porters with fossils. In fact, a very large part of Tropical Africa 

 appears not to have been below the level of the sea since geological 

 history began, and even its lacustrine deposits have yielded, as yet, 

 . nothing of palaeontological interest. But there is much to reward the 

 physical geologist. The country traversed by Dr. Gregory consisted 

 first of the coastal plain, marshy and malarious, but m the British 

 dominions fortunately narrow enough to be crossed in a couple of 

 marches ; then of a zone of foot-hills, also narrow. This is followed by a 

 higher and very broad zone, a sandy, barren district, mostly covered 

 with ' scrub.' To this succeeds the ancient backbone of the continent, 

 a highland region of very old rocks which may be traced from the 

 Drakensberg of Natal to the mountains of Abyssinia ; possibly even 

 through Eastern Egypt as far as Cyprus. Then comes the great zone 

 of volcanic rocks — wide-spreading sheets of lava, which are crowned 

 here and there by huge cones such as Kilima-Njaro and Kenya, and 

 this is followed by a region, once also highland, but now broken by a 

 series of north and south faults into the * Great Rift Valley.' Its 

 floor consists of " ancient and modern lavas of various ages, the 

 alluvium of dried lake basins, recent river gravels, and deserts of loose 

 drifting sand." Dr. Gregory was struck by the resemblance between 

 the lava-plains and those about the Snake River of Idaho, and con- 

 siders these to have been produced by the combination of eruptions 

 from numerous centres, which he proposes to call ' plateau eruptions,' 

 rather than by outpourings from fissures. 



But the phenomena afforded by the Rift Valley are yet more 

 interesting to the student of physical geology. The African lakes, as 

 Dr. Gregory points out, fall naturally into two classes : one long and 

 narrow, lying like fjords between steep cliffs ; the other rounded in 

 shape and with low shelving shores. Lakes of the former class occur on 

 two lines, which pass on either side of the Nyanza and meet at Lake 

 Rudolf. " Thence the line continues northward as a long strip of low 



