148 THE DESTCCATIOX OF LATER OEOLOGICAL TIMES. 



position on the formation of desert regions ; and later investigations, like 

 those of Diivejrier, Dr. Mares, and Vatonne, made on the spot, in regard to 

 the formation of sand dunes, as well as those of Hann and WojeikofFon the 

 influence of meteorological conditions on the desert surface, render the con- 

 ception of the desert as the product of climato-meteorological changes more 

 and more probable. It is not intended, however, by this, to assert that, 

 during the latest geological period, numerous larger and smaller inland lakes 

 may not have existed in the Sahara ; on the contrary, we are obliged to 

 recognize the numerous sebchas and dayas as the remains of such fresh- or 

 brackish-water collections. In the Western Sahara, at all events, these lakes 

 did not have any great extension during the Quaternary epoch, and they 

 were separated by the previously mentioned range of elevations from the 

 great inland sea, which occupied the place of the present sea of sand of the 

 Libyan Desert. The correctness of this view appears to be fully confirmed, 

 by the fact that, up to the present time, no marine deposits or fossils have 

 been found in the western basin, while such are by no means wanting in the 

 Libyan Desert. 



" In the present distribution of certain animals we find strong reasons 

 for believing that, even in historical times, the Sahara was less extensive 

 and less of a desert than it now is. First ; the late introduction of the 

 camel, which was not domesticated in Northern Africa luitil one or two 

 centuries after the birth of Christ. Again ; there must have been in the 

 Southern Atlas, in ancient times, numerous wild elephants, since we know 

 that the Carthaginians caught their war-elephants within their own territory. 

 So, too, the hippopotamus existed in a region where now it could not, by 

 any means, find sufficient water, the same being the case Avith the elephant 

 as respects food. Crocodiles, which in former times occurred in prodigious 

 numbers, were also supposed to have died out ; but, not long since, a French 

 traveller. Baron Aucapitaine, found some still living in the Wadi-el-Dscheddi ; 

 and, still more recently, Edwin von Bary proved their existence in the 

 uninhabited valley of Mihero, on the Tasili plateau. The former occurrence 

 of all these animals in the Northern Sahara, which in its present condition 

 would present an insurmountable barrier to their introduction from the 

 South, renders the adoption of the hypothesis of a former more luxuriant 

 vegetation and m.ore abundant precipitation where now there is only desert, 

 a matter almost of absolute necessity. In general it may be said that, south 

 of the 34th parallel, in this region, there has been a constant advance of the 



