THE SAHARA. 147 



imposed on them by the desert nature of a country where only an occa- 

 sional oasis can, by artificial irrigation, be made to bear fruit enough to give 

 a scanty suppoi't to a limited population. 



Dr. Chavanne has, so to speak, monographed the Sahara,* and given a 

 very complete resume of all that has been found out about that region up to 

 a very recent date. His views, which appear to the present writer to be, in 

 the main, justified by the facts, may be inferred from the following quota- 

 tions : " Up to the most recent period, it was generally thought to be a fact 

 which could not be controverted, that the Sahara had been, dui-ing the most 

 recent geological period, one great inland sea, and that, consequently, the 

 dunes, or accumulations of sand of the present sea of that material, which 

 cover the region, were the relics of that sea. The existence of numerous 

 schotts, sebchas and salt morasses, the discovery of brackish-water shells 

 ( Cardium edide) in the northern part of the Sahara, at an elevation of from 

 200 to 300 meters, seemed to prove the ti'uth of this theory beyond possi- 

 bilit}' of dispute. The well-known German geologists, Desor and Escher 

 von der Linth. who in 1863, in company with Professor Martins, of Mont- 

 pellier, made a journey to the Algerian Sahara, published results of their 

 observations which appeared to confirm the hypothesis in question ; and 

 De.sor carried the theory still fiirther, inasmuch as he endeavored to show 

 that the Sahara was the ffrand regulator of the climate of South and Middle 

 Europe, and to connect the extension of the Alpine glaciers with the former 

 watery covering of Northern Africa. However enticing [verlockend] this 

 theory may be, it is not supported by the facts. The first impression which 

 the traveller gets of the desert, especially when standing on the southern 

 slope of the mountains bordering the Sahara on the north, is indeed highly 

 favorable to the hypothesis of a former occupation of this region by the sea. 

 The writer himself, when visiting the northern edge of the desert, was led 

 to look on this theory as most probably correct. An exhaustive and un- 

 prejudiced examination of the mode of formation of the sand accumulations, 

 the consideration of indisputable facts, such as the existence of crocoddes 

 in the heart of the Sahara, and of petrified forests in the Libyan oases, can- 

 not but lead to the conclusion that the present sandy regions owe their 

 existence to some other cause than that of a former universal water cover- 

 ing. Humboldt long ago recognized the influence of general geographical 



* In his volume entitled "Die Sahara, odev von Case zu Case." Wien, 1879. See also another later work, by 

 the same author, " .-Vfrika ini Lichte unserer Tage." Wien, 1881. 



