146 THE DESICCATION OF LATER GEOLOGICAL TIMES. 



sterility. As on the eastern borders of the Mediterranean, so farther west, 

 there are abundant evidences of tlie former presence of nations possessing a 

 much higher grade of civiUzation than that of the present population, whose 

 numbers have dwindled with their diminisliing intelligence, and whose habits 

 and modes of life, while eminently suited to the physical conditions by which 

 they are surrounded, are beyond a doubt incompatible with what is now 

 called civilization. Everywhere the ruir.s of former greatness are to be seen, 

 offering a striking contrast to the present struggle for mere existence neces- 

 sitated by the diminished area susceptible of cultivation, and the impossi- 

 bility of procuring a sufficient supply of water for irrigation, except in a few 

 favored localities, of exceedingly small dimensions as compared with the 

 extent of the surrounding desert. 



The recent explorations of the Sahara have resulted in the correction of 

 some of the former erroneous impressions prevailing in regard to the real 

 causes of the increased dryness of that region. The examinations made 

 by Desor of a limited area, on the northern edge of that part of Africa 

 known as the Desert of Sahara, led him to form the idea — which, for a 

 time, was very generally adopted — that the whole of this vast region had 

 formerly been covered by the sea, and that it had been raised above water 

 during the very latest portion of the Tertiary epoch. This elevation of the 

 land, according to Desor, brought about not only the dryness of the Sahara 

 itself, but had a powerful influence in putting an end to the phenomena of 

 the glacial epoch, as will be mentioned farther on. 



It is now known, however, that only a small part of the Sahara has been 

 covered by the sea at any period since the Cretaceous epoch. On the con- 

 trary, we find everywhere abundant proof of the former presence of fresh 

 water, which stood in lakes or ran in rivers; and, of course, a corresponding 

 amount of evidence that there has been a marked change of climate during 

 recent periods. In fact, there seems to be little doubt that this change, 

 whenever begun, has been continued during the historic period, the kind of 

 evidence furnished by recent investigators being precisely similar in charac- 

 ter to that already brought forward in reference to Syria, Egypt, and the 

 Libyan desert. The remains of buildings of various dates, as well as the 

 records of history, show conclusively that large ]iortions of Northern Africa 

 were once much more thickly populated than they now are ; but that the 

 stage of civilization then reached was far higher tlian that of the present 

 inhabitants, whose mode of life is strictly in accordance with the conditions 



