May 



1903] 



NATURE 



57 



I 



loore at 13,500 feet, and some of the peaks he thinks 

 lay attain a height of 16,500 feet, while Sir Harry 

 jhnston believes that 20,000 feet is a probable mini- 

 lum of the height of some of them. This great 

 lountain chain, giving rise in some parts of its course 

 numerous glaciers — the " Mountains of the Moon " 

 ^f the ancients — Mr. Moore proposes to call " the 

 reat Central African Chain." It extends from the 

 lountains of Abyssinia in the north to the Drakens- 

 jrg in South Africa, though in some places, as in the 

 ^neighbourhood of Tanganyika and the Albert Edward 

 Xyanza, it is a broad ridge, the culmination of long 

 eastern and western slopes, rather than a conspicuous 

 chain ; so that, viewed from either side, it has little 

 resemblance to a mountain range, even when its 

 >ummits rise ten or twelve thousand feet above the sea- 

 level. 



Mr. Moore discusses the geological structure of this 

 L^reat mountain chain, giving a number of valuable 

 _:i ological sections across it at various points. The 

 I igin of the range, he believes, must be assigned to 

 lateral compression, the celebrated " rift-valleys " being 

 regarded by him as subordinate features resulting from 

 the orographic movements in the earth's crust. Al- 

 though volcanic action has only played a subordinate 

 part in the formation of the great chain itself, in the 

 i^reater portion of its course, yet in the district lying to 

 the north of Tanganyika, which was carefully explored 

 by our author, we have the still active volcanic district 

 of the Mfumbiro Mountains, a chain of volcanoes 

 running east and west; the highest of these, Kari- 

 simbi, is often snow-capped, and has a height of 14,000 

 ■feet. Mr. Moore shows that the structure of the 

 great longitudinal valley in which Tanganyika lies 

 has been profoundly modified by the ejection of the 

 materials forming the Mfumbiro chain. The surface 

 of Lake Kivu, to the north of Tanganyika, is 4841 

 feet above sea-level, while Albert Edward Nyanza, still 

 further north, lies 2000 feet lower, and Tanganyika 

 has a height of 2700 feet. The author points out that 

 previously to the formation of the Mfumbiro volcanic 

 cones, the waters of Lake Kivu must have drained 

 northwards into the Albert Edward Nyanza, and not, 

 as now, into Lake Tanganyika, by the Russisi River. 

 Numerous other volcanic cones occur in the district, 

 generally at the bottom of the rift-valleys. The waters 

 of Lake Kivu contain such a large amount of salts 

 that the pebbles and reeds on the shores become en- 

 trusted with a calcareous deposit, which analysis shows 

 to contain 12.66 per cent, of magnesium to 28.65 of 

 calcium. The waters of Lake Kivu, which is some- 

 times more than 100 fathoms deep, have been analysed 

 and found to contain a very large proportion of mag- 

 nesium carbonate. 



The geological formations met with in the expedi- 

 tions, the distribution of which in the neighbourhood 

 of the several lakes is shown upon sketch-maps, are 

 as follows, beginning with the oldest : — 



(i) Old crystalline rocks — granite, gneisses, schists, 

 quartzite, &c. 



(2) Great thickness of unfossiliferous sandstones and 

 shales. 



(3) " Drummond's beds," a series of sandstones and 

 shales of about the age of the Trias. 



(4) Recent lacustrine strata. 



Unfortunately, no satisfactory evidence has yet been 

 adduced as to whether the stratified rocks (2) and 

 (3) can, either or both of them, be regarded as of 

 marine origin, and some of the unsolved problems of 

 African geology must await full solution until this 

 determination has been made. At present we have no 

 proof that the stratified masses of the older formation 

 are not, like those of the younger, of lacustrine or 

 fluviatile origin. 



NO. 175 1, VOL. 68] 



Around some of the great Central African lakes there 

 are found extensive alluvial deposits containing the 

 shells of species of Mollusca, which still live in the 

 waters of the adjoining lake. These, with the 

 numerous raised beaches, show that some of the lakes 

 had formerly a much greater extent than at present. 

 It is upon these old alluvial deposits that the celebrated 

 " Park-lands," so well described and so convincingly 

 explained by Mr. Moore, are found. Among the 

 botanical results of the two Tanganyika expeditions, 

 not the least valuable are. the investigation of these 

 curious features thgt have attracted so much attention 

 from all travellers in the district. Mr. Moore shows 

 how the springing up of scattered individuals of the 

 hardy euphorbias has afforded a shade under which 

 plants less able to withstand the burning heat of the sun 

 have grown up and gradually extended outwards. Of 

 course, in the end, these outward spreading patches ol 

 vegetation must coalesce and form a tangled forest 

 growth, such as occurs in other parts of Central Africa. 

 Mr. Moore ingeniously argues that the amount of de- 

 velopment towards this forest growth may be utilised 

 as a means of determining the geological age of the 

 alluvial flats upon which they are found. 



It is on the zoological results of these expeditions, 

 however, that the author of the work before us must 

 be especially congratulated. The addition of nearly 

 200 species of animals to the fauna of the district 

 is the least important of his achievements, though 

 it shows how assiduous and successful must have 

 been his work as a collector. But Mr. Moore is 

 far more than a collector. By careful observations and 

 experiments carried on during his residence among the 

 lakes, by his studies of living animals in their peculiar 

 environment, and by his work in the laboratory upon 

 the specimens he has brought home, he has made the 

 most substantial additions to zoological science. 



On questions of distribution the researches of Mr. 

 Moore have a very important bearing. The discovery 

 by Speke and the missionaries of marine types of 

 mollusca in the waters of Tanganyika, followed as it 

 was by Boehm's discovery of a medusa in the same 

 fresh waters, made it a question of first importance 

 to determine whether the same phenomena were ex- 

 hibited in any other of the African lakes. To this 

 question Mr. Moore has afforded a complete answer. 

 He has himself examined the faunas of lakes Shirwa, 

 Nyassa, Kela, Tanganyika, Kivu, the Albert Edward 

 Nyanza, the Albert Nyanza, the Victoria Nyanza, and 

 Nivasha. The faunas of four or five more lakes are 

 less perfectly known from the work of other travellers, 

 and it is now certain that the peculiar " halolimnic 

 fauna," as Mr. Moore calls it, is confined to Tangan- 

 yika, all the other neighbouring lakes containing only 

 the ordinary types of fresh-water mollusca and fish 

 that occur in similar situations all over the globe. The 

 account given of the distribution of these forms by Mr. 

 Moore, especially in the salt lake of Shirwa, will prove 

 of interest both to zoologists and to geologists. 



The fish-fauna of Tanganyika consists of eighty- 

 seven species, of which no less than seven t)^-f our are 

 new to science, and have been described and figured 

 by Mr. Boulenger. The medusa (Limnocnida tangan- 

 yicae) of Tanganyika has been described from spirit 

 specimens by Mr. Robert Giinther, of Oxford ; but Mr. 

 Moore has been able, during his residence at the lake, 

 to make drawings of the living animal, to work out 

 its development, and to add much to our knowledge 

 of its habits. We reproduce his drawings of this 

 curious organism, which varies in size from a shilling 

 to a two-shilling piece. 



The complete study of the anatomy of the " halo- 

 limnic " gasteropods, which so closelv resemble marine 

 forms of the Jurassic period, has been carried out by 



