HIGH SCHOOL ZOOLOGY. 279 



within the Arctic Circle (where, as we know from fossils found, 

 there had been warm seas during the Miocene epoch,) had the 

 effect of producing the glaciation It must not be supposed 

 that the Glacial Period lasted with undiminished severity dur- 

 ing all this time ; we have evidence of interglacial milder 

 periods, when the Ice-Sheet retired, and the life, which had been 

 driven towards the south, again crept northward, but these very 

 alternations must have been a fruitful source of change in the 

 fauna and floi-a of the countries subjected to them. 



15. Apart from the combined effects of the astronomical con- 

 ditions referred to, and the raising of the land towards the North 

 Pole, let us consider the effects of a general elevation of the sea- 

 bottom outside the present shore-line, to an extent far less than 

 we know to have taken place within comparatively recent times. 



The summits of some of the Alps — the Dent du Midi, for 

 example, 10,770 feet — are formed of Nummulitic limestone, a 

 formation consisting largely of shells of Foraminifera, deposited 

 during the middle Eocene epoch, and elevated since then. Now, 

 we know from hydrographic researches that if an elevation of the 

 shallower waters of the world to half tliis extent were to take 

 place, that it would entirely alter the configuration of the land. 

 Not only would Great Britain be continuous with France, Den- 

 mark and Norway, but the whole of Europe, Africa and Asia 

 would form one continuous Continent. It would be even possible 

 to travel by land from England to Canada, via Iceland, Green- 

 land and Labrador, and then on to Siberia by Alaska. The only 

 large tracts of land remaininc; unconnected with this vast Con- 

 tinent would be Australia, which would still be an Island, and 

 Madagascar, which would still be separated from Africa. 



Ample evidence exists, and some of it has been already re- 

 fei-red to {VI. ;iO), which shows that changes of such a character 

 have occurred, not necessarily simultaneously, but at least at 

 different times. The Camel family, e.g., flourished in North 



