3 1 6 The Scottish Naturalist. 



immigrated from Scotland and England by a land-connection, 

 the whole country standing higher out of the water than at 

 present, transforming the Irish Sea into a lake. The first plants 

 to occupy Ireland of course would be the arctic alpines, which 

 had only time to partially take possession when a gradual sink- 

 ing of the land took place, cutting off the connection with 

 Britain, and necessarily also the immigration of the flora, which 

 would then be driven up the hills by the advance of the sea. 

 Once more came another upheaval of the land, again connect- 

 ing Ireland with Britain, over whose area by this time the 

 amelioration of the climate had caused the Germanic or lowland 

 flora to be on the rapid march westward. This flora accordingly 

 was now gradually finding its way into Ireland, which, however, 

 before the immigration was complete, once more became iso- 

 lated, and has so remained ever since. Hence the compara- 

 tively limited fauna and flora of the Green Isle. 



Dr James Geikie says : 1 "It is perhaps owing to the late 

 appearance of the land-connection that the Scandinavian type 

 of vegetation is so poorly represented in the Hibernian flora. 

 The climate, we may suppose, was already become milder, and 

 the high alpine forms were gradually vanishing from the low 

 grounds, so that only a few of these could make their way south 

 into Ireland." 



The geographical, physical, and climatal changes we have 

 been speaking of were, it may be imagined, very gradual, and 

 occupied long periods of time. And as there were what geolo- 

 gists term interglacial periods — that is, a warm or temperate 

 period, then a return of glacial conditions more or less severe — 

 the process of redispersal and redistribution of the fauna and 

 flora was repeated. 



Wherever species were originally created, or evolved, as some 

 would have it, these changes were the means of their distribu- 

 tion into other countries where soil, climate, and other condi- 

 tions were found suited to their wellbeing, although many 

 species have a wonderful adaptability to change of circumstances 

 and surroundings, and often themselves thereby undergo a 

 change in their habit and appearance, even, according to some 

 high authorities, to the extent of becoming new species. 



Suppose certain species transferred from one locality where 

 the summer is hot and short and the winter long and severe, 

 and where, during the greater part of the year, they are covered 



1 ' Prehistoric Europe.' 



