xvi PREFACE. 



To sum up our deductions, a review of the botany as well as the 

 zoology of the Dead Sea basin reveals to us the interesting fact that we 

 find in this isolated spot, comprising but a very few square miles, a series 

 of forms of life differing decidedly from the species of the surrounding 

 region, to which they never extend, and bearing a strong affinity to the 

 Ethiopian region, with a trace of Indian admixture. 



In order to form a just conclusion as to the mode by which this 

 isolated region became peopled by animals and plants, it is necessary to 

 take geological causes into consideration. Here is a patch of tropical 

 character, containing southern forms so peculiar and unique, that we can- 

 not connect their presence in it with any existing causes or other trans- 

 porting influences. The basin, at the bottom of which they are found, is 

 a depression in a mountainous country, sunk 1,300 feet below the level of 

 the ocean, and occupied, with the exception of a few acres here and there, 

 by the waters of a salt lake. It is hemmed in by two parallel mountain 

 ranges, rising from 3,000 to 5,000 feet above its level, and these enclosing 

 ranges are rarely more than 20 miles apart. 



As it has been shown by Humboldt that zones of elevation on moun- 

 tains correspond to parallels of latitude, the higher zones corresponding 

 with the higher latitudes, so here we find a zone of depression, the only 

 one known to us, producing similar phenomena, and exhibiting in generic 

 correspondence, specific representation, and in some instances specific 

 identities, the fauna and flora of much lower latitudes. As the flora and 

 insect fauna of the Scottish mountain tops is Scandinavian, while the 

 surrounding type is German, so we find this islet of Ethiopian flora in the 

 midst of a Mediterranean district. If we had to deal only with a repre- 

 sentative flora, it might have been assumed that it essentially depended 

 on the law that climatal zones of animal and vegetable life are naturally 

 repeated by elevation (in this case depression) and latitude. But the 

 transmission of a transported flora requires another explanation, which 

 can only be found by tracing geological history. That it became peopled 

 by special creation within this area, or that its inhabitants can have had 

 an independent origin on the spot, would not only be a most unreasonable 

 assumption, but is negatived by the fact of the identity of many species of 

 animal life, and of almost the entire flora, with species now living in the 

 Ethiopian region. 



