522 Hevieics — Geological Survey Memoirs. 



ascended, would liave proved an effectual barrier towards the south.^ 

 Towards the west the barrier would have been much more elevated. 

 Hence the living forms in the waters of the inland salt lake were 

 isolated from those of the ocean, and had either to adapt themselves 

 to their new conditions or to die out. 



We may suppose that the first to disappear would be the corals, 

 crinoids, and starfishes. On the other hand, fishes, molluscs, and 

 crustaceans, having greater powers of adaptation, would in many 

 cases survive. Meanwhile, the law of "descent with modification " 

 would now come into operation, and we may suppose that through- 

 out the Miocene and Pliocene periods the process of modification in 

 form, colour, and habit gradually proceeded. The fittest forms 

 survived, and differentiation between those of the outer and inner 

 seas, resulting, as we have seen, in almost an entire specific change, 

 was efiected. 



The above view seems in accordance with recent observations 

 regarding the adaptability of many marine forms to new lacustrine 

 conditions, provided the process of change is sufficiently gradual. 

 Professor Sollas, whose memoir on "The Origin of Fresh-water 

 Faunas"^ is very suggestive, arrives at the conclusion that, as the 

 conversion of comparatively shallow continental seas into fresh- 

 water lakes has taken place on a large scale several times in the 

 history of the earth, this has been accompanied by the transforma- 

 tion of some of the marine into fresh-water forms. The Jordan 

 valley lake, originally salt, has shrunk back into two or three lakes 

 connected by a river. The Dead Sea alone remains salt and lifeless. 

 The waters of the Sea of Galilee are fresh, and teem with life. In 

 reply to my enquiry whether the above views would harmonize with 

 his own. Professor Sollas writes : " I have always regarded the 

 curious fishes of the Sea of Galilee as evidence of a previous marine 

 communication, but it never occurred to me to speculate as to the age 

 of that connection. If this sea (that of Galilee) were stocked from 

 the Eocene ocean, it would fit in very well with the history, as I 

 believe it, of other fresh-water faunas." It is gratifying to me to 

 have the concurrence on this point of so able an authority. I conclude, 

 therefore, that the special forms of fishes now inhabiting the Sea of 

 Galilee are the descendants of those which lived in the Eocene ocean. 



I^ E "V" I IB -v^ S. 



The Geology of the Country abound Ipswich, Hadleigh, 

 AND Felixstow. By William Whitaker, B.A., F.G.S., etc. 

 (With Notes by W. H. Dalton, F.G.S., and F. J. Bennett, 

 F.G.S.) Memoirs of the Geological Survey. 8vo. pp. vii. 156. 

 London, 1885. Price Two Shillings. 



ri^PIIS Memoir contains a detailed account of the formations that 

 JL are met with in the country around Ipswich, or in the tract 

 embraced by Quarter-sheets 48 N.W. and N.E. of the Geological 

 Survey Map. 



1 See Mount Seir, Sinai and "Western Palestine, pp. 95 and 99, etc. 



2 Scientific Trans. Hoyal Dublin Society, vol. iii. ser. 2. 



