hortensis, with a similar European distribution, has also probably 

 entered Ireland from the north. You will notice from the map 

 that it has succeeded in gaining access to the Faroes, Iceland, 

 Greenland, Labrador, and even the north-eastern parts of the 

 United States, probably at a time when an ancient land-bridge 

 extended right across from Europe to North America. 



Then we have in Ireland groups of northern forms of animal 

 life which all seem to have passed into the country from the 

 north. Thus the Beetle, Pelophila borealis, has a very dis- 

 continuous range in Scotland; in Ireland it. is quite confined to 

 the north and west ; in England it is absent altogether. There is 

 another similar example — the Arctic Dragon-Fly, Somatochlora 

 arctica. It inhabits in the British Islands only a few isolated 

 spots in Scotland and a single locality in the west of Ireland. 

 Similar instances among the Mammals are, as I have already 

 mentioned, the Irish Hare and the extinct Lemmings and 

 Reindeer. They must all have entered Ireland from the north. 



Let us now picture to ourselves what Ireland looked like 

 when it was joined to England and the Continent. If we imagine 

 the bed of the Irish Channel to be raised by only a few hundred 

 feet, we should have a vast stretch of dry land across which could 

 stream the fauna of England and Scotland. But we know from 

 a study of the admiralty charts of the depths of these seas, that 

 this land would not be one level plain. Some parts of the Irish 

 Channel are much deeper than others. Somewhere about the 

 middle between Ireland and England there exists a long stretch 

 of deep water. If the sea bed were raised all the rivers that now 

 drain into the Irish Sea would send their waters into this hollow, 

 with the result that we should have a great lake extending for 

 more than a hundred miles between England and Ireland. At 

 such a period there would be at the southern end of this lake an 

 extensive plain occupying the region between the south-west of 

 England and the south of Ireland. I fancy that the bulk of the 

 southern fauna would have travelled across this plain from the 

 north-west of France to Ireland. 



