xx PREFACE. 



Dead Sea sand, such as Gr. capreolus, we have the relics of the inhabi- 

 tants of that early sea. But of the Hving inhabitants, we must place the 

 Jordanic fishes as the very earliest, and these, we have seen, form a group 

 far more distinct and divergent from that of the surrounding region than 

 in any other class of existing life. During the epochs subsequent to the 

 Eocene, owing to the unbroken isolation of the basin, there have been 

 no opportunities for the introduction of new forms, nor for the further 

 dispersion of the old ones. These forms, as we have seen, bear a striking 

 affinity to those of the freshwater lakes and rivers of Eastern Africa, 

 even as far south as the Zambesi. But the affinity is in the identity of 

 genera, Chromis and Heiiiichromis being exclusively African, while the 

 species are rather representative than identical. 



The solution appears to be that during the Meiocene and Pleiocene 

 periods, the Jordan basin formed the northernmost of a large system of 

 freshwater lakes, extending from north to south, of which, in the earlier 

 part of the epoch, perhaps the Red Sea, and certainly the Nile basin, the 

 Nyanza, the Nyassa, and the Tanganyika lakes, and the feeders of the 

 Zambesi, were members. During that warm period, a fluviatile ichthyo- 

 logical fauna was developed suitable to its then conditions, consisting of 

 representative and perhaps frequently identical species, throughout the 

 area under consideration. 



The advent of the glacial period was, like its close, gradual. Many 

 species must have perished under the change of conditions. The hardiest 

 survived, and some perhaps have been gradually modified to meet those 

 new conditions. Under this strict isolation it could hardly be otherwise ; 

 and however severe the climate may have been, that of the Lebanon 

 with its glaciers probably corresponding with the present temperature of 

 the Alps at a proportional elevation (regard being had to the difference 

 of latitude), the fissure of the Jordan being, as we certainly know, as 

 much depressed below the level of the ocean as it is at present ; there 

 must have been an exceptionally warm temperature in its waters in which 

 the existing ichthyological fauna could survive. 



The glacial period has left its mark in the mountain range of Northern 

 Palestine, not only in the moraines which stud the Lebanon ; and the 

 desolate heaps of which point out the position of the old glaciers as 

 shown by Sir J. D. Hooker ; but even in the existing forms of life. 



