548 Bulletin American Museum of Natural History [Vol. LITT 
disappearance was mainly due to silting up, as shown by the thick alluvial 
deposits now found in the areas which they formerly occupied. For it 
must be remembered that many of the coastal effluents even nowadays 
flow through narrow and deep gorges where their course is more or less 
interrupted by rapids and falls. In the case of the Congo basin, for 
instance, we assume that the lower, central portion was occupied by an 
extensive, but relatively shallow, body of water, of which Lake Leopold 
II, Lake Tumba and Stanley Pool are the remnants. We have traced 
the limits of this ‘‘Congo lake”’ at the present contour-line of 1,500 ft. 
(Stanley Pool is now 931 ft. above sea-level) and there are in the region 
of the cataracts where the lower Congo crosses the Crystal Mountains, 
many spots where such an altitude is reached right on the cliffs or steep 
hills that fringe the stream.! Quite apart from the tapping of these late 
Pleistocene lakes by coastal effluents, the gradual desiccation of the con- 
tinent—due to a climatic change—also contributed to reduce their size 
through increased evaporation and decreased inflow. Lake Chad, Lake 
Bangweolo, and Lake Ngami are vanishing evidences of former lacustrine 
basins and in the other areas similar, though smaller, remnants may be 
traced.” | 
The gradual drying up of Africa has been frequently discussed of 
late and we do not intend to go at length into this subject.2._ There can 
1The lowering of the region of the Crystal Mountains through erosion since the Pleistocene must also 
be taken in account in trying to gain an idea of the level which the Central Congo lake may have reached 
before it was connected with the Atlantic. 
*See Anon. (after R. Williams). 1907. ‘The,Okavango and theformer Lake Ngami.’ Geograph. 
Journ., London, XXX, pp. 440-441. 
Audouin. 1905. ‘Notice hydrographique sur le lac Tchad.’ La Géographie, XII, pp. 305-320. 
ee W. 1921. ‘The encroachment of the Sahara on the Sudan.’ Journ. African Soc., XX, 
pp. =185. . 
os ice ae R. 1919. ‘La capture du Niger par le Taffassasset.’ Ann. de Géographie, No. 151, pp. 
Gate bale ‘L’hydrographie ancienne du Sahara.’ C.R. Ac. Sci. Paris, CLX XII, pp. 457-460. 
1921. ‘Les changements de climat du Sahara pendant le quaternaire.’ C.R. Ac. Sci. Paris, 
CLX XII, pp. 604-607. % 
_ 1921. ‘L’hydrographie ancienne du Sahara (Les conséquences biogéographiques).’ Revue 
Scientif., No. 8, pp. 1938-198, 1 map. 
1921. ‘Le probléme du desséchement en Afrique occidentale.’ Bull. Comité Et. Hist. Scientif. 
Air. Occ. Frang., No. 3, pp. 853-369. 
Germain, L. 1909. ‘Recherches sur la faune malacologique de l’Afrique équatoriale.’ Arch. Zool. 
Expér. Gén., XLI, pp. 1-195, Pls. I-11 (see especially pp. 66-77). 
Harger, R. L. 1917. ‘The desiccation of Africa.’ Journ. East Afr. Uganda Nat. Hist. Soc., t's 
11, pp. 142-152. 
Hobley, C. W. 1916. ‘The alleged desiccation of East Africa.’ Op. cit., V, 9, pp. 4-16. 
_ Hubert, H. 1920. ‘Le desséchement progressif en Afrique occidentale.’ Bull. Comité Et. Hist. 
ete Afr. ee Franc., pp. 401-467, Pls. -1v. 
arquardsen, H. 1916. ‘Tschad-See und Bahr-el-Ghazal (Soro).’ Mitt. Deutsch. Schut: : 
XXT a ee ( ») i eutse chutzgeb., 
Migeod, F.W.H. 1922. ‘Some notes on the Lake Chad region in British territory.’ G 
J outa. Hee TGS Sore. oe Fj i siagohe re sph. 
ellegrin, J. 1921. ‘Sur des otolithes subfossiles de poissons du Sahara méridional et 1 ionifi- 
cation,’ C.R. Ae. Sel, Paris, CLXXIL, pp. 774-776. oe 
iercy, W. C. 1906. ‘The fall of the Central African lakes: Lake N OE h. 
London, RVIIT pp. 641-643. yasa eograph. Journ. 
chwarz, E. H. L. 1918. ‘The progressive desiccation of Africa: the ca d th : 
South African ay Bet Re pp. 1389-178. eae sie Liam 
1920. ‘The Kalahari or thirstland redemption.’ (Cape Town), vi+163 pp., 14 Pls., 3 maps. 
_, 1921. ‘The control of climate by lakes.’ Geograph. Journ., LVII, pp. 166-174. “a 
Tilho, J. 1906. ‘Exploration du lac Tchad.’ La Géographie, XIII, pp. 195-214, map. 
