512 



PREHISTORIC EUROPE. 



point between Braich-y-pwll in Caernarvon and Greenore Point 

 in Wexford. 1 This lake, receiving the tribute of many Scottish, 

 Irish, and English streams, would discharge a broad river from 

 its lower end, which might well be impassable by many of the 

 smaller vertebrates. That it was rather the presence of this lake 

 and the obstacle of the Welsh Mountains than the premature 

 appearance of the Irish Sea which arrested the westward migra- 

 tion of plants and animals, is shown by the remarkable fact 

 pointed out by Professor Leith Adams, 2 that the mammalian 

 fauna of Ireland agrees more closely with that of Scotland than 

 of England ; while Dr. Buchanan White has shown that Ireland 

 has probably derived some of its alpine lepidoptera from Scot- 

 land. We may suppose that the temperate mammals gained 

 admittance to Ireland from the west of Scotland, between which 

 and the north of Ireland there was a broad land -connection. 

 Some of the larger mammals, however, such as the great Irish 

 deer (Cervus megaceros), may quite well have entered Ireland 

 from the south, crossing the river that flowed south through St. 

 George's Channel. But it may be questioned whether the rein- 

 deer immigrated by the same route. So far as the geological 

 evidence goes, we have no reason to believe that at the com- 

 mencement of the postglacial period the British area was much 

 more extensive than it is at present. The sea was then retiring, 

 as we know, from the low grounds of Southern Scandinavia and 

 Scotland, and from the borders of East Anglia, and thus the 

 probabilities are that when the Scandinavian flora had com- 

 menced its northward advance St. George's Channel still separated 

 England and Ireland. This being so, the reindeer could not at 

 that time reach the latter country. By and by, however, the 

 Irish Sea gradually disappeared, and a land- connection took 

 place between Scotland and Ireland, across which the alpine and 

 sub-alpine flora and the reindeer would migrate. It is perhaps 

 owing to the late appearance of this land-connection that the 



1 See Admiralty's chart of East Coast of Ireland, No. 1824a; and Great Ice 

 Age, Plate xii. 



2 Proc. Royal Irish Acad., 2d Series, vol. iii. p. 99 ; Proc. Royal Dublin Soc, 

 1878, p. 42. 



