76- John G'unn — Causes of Change of Climate. 



the increasing cold, arising from the elevation of the land, would not 

 only have prevented their passage over, but have caused the extermi- 

 nation of all the Elephants, except indeed the £. antiquus and E. 

 primigeniiis. 



With respect to the Molluscs, the same story is told by them. Sir 

 C. Lyell ^ has identified specimens from the Red Crag at Walton-on- 

 the-Naze, in Essex, with some now living in the Mediterranean, and 

 the Cyrena or Corhicida fluminaUs, ouce common in the Norfolk Crag- 

 beds, is now not to be found nearer than in the warm waters of the 

 Nile. 



It thus a]3pears that both Mammals and Molluscs have had an 

 extensive range before the mountain heights were upheaved, and 

 intercommunication cut off. It may seem startling to affirm that the 

 Alps have been interposed at so late a geological period. We are 

 accustomed to regard them as monuments of the highest geological 

 antiquity, on account of their sub-strata of Primary rocks ; but never- 

 theless, as Sir Roderick Murchison has shown ^ in his able paper on 

 the " Structure of the Alps," they have been comparatively recently 

 elevated, so that not only Miocene, but Pliocene formations rest upon 

 their present summits ; and probably still more recent deposits have 

 been laid upon them, and have been worn down by the process of 

 glaciation. 



The effects produced by the elevation of the Alpine ranges is 

 obvious. The extreme cold induced culminated in the almost entire 

 change of the fauna. The Elephas primigenius and the Bhinoceros 

 ticliorhinus survived and superseded the other and more southern 

 types ; the Cervus elephas, C. tarandus and the C. ca'preolus survived 

 the profusion of Deer whose remains are yielded by the Forest-bed, 

 and also a host of other Mammals, which succumbed to the cold. 



The Glacial epoch, so called, was thus introduced, and the moun- 

 tain heights, when they attained their highest point of elevation, 

 spread their refrigerating influence far and wide by an ice-sheet, or 

 glaciers, descending into the plains. This was necessarily limited 

 by, and proportioned to the degree of latitude, while near to the 

 Pole, the ice would be continuous, and icebergs, carried down into 

 the sea, would extend the cold into otherwise warmer regions. 



The reality of this cause of cold is best shown by the effect pro- 

 duced by the opposite system of depression and the gradual diminu- 

 tion of the regions of perpetual ice and snow. 



Every traveller in Switzerland, Savoy, Italy and Greece remarks 

 the traces of former glaciation and of retreating glaciers. In France 

 the return to a genial climate is evident, as in Dordogne, where 

 the Reindeer and the Elephas primigenius once lived, and have left 

 their relics, and their unmistakable portraits, or figures carved by 

 the hands of former natives. 



Such are some of the indications of the change of climate from 

 cold to warmth due to the gradually diminishing height of mountain 



1 Elements of Geology, p. 207, 6th edition. 



2 Quart. Journ. Geol. Sue, vol. v. p. 244, 



