Mr Harme-Brovm on the Squirrel in Great Britain. 41 



became scarce in Dumfriesshire at many localities, and 

 elsewhere in the south of Scotland ; whereas, in Perthshire, 

 " never had they been so abundant as they were in the 

 winter of 1879-80." They have fled the more exposed 

 places, and sought the shelter of the larger tracts of forest 

 and of larger food supply. I have many correspondents' 

 letters remarking upon these facts ; so the severe effects of 

 the winter of 1878-79 produced their mark on the squirrel 

 population of 1879-80. 



These considerations certainly lead up to the same results 

 which have been so clearly pointed out by my friend Mr E. 

 E. Alston, in his admirable account of the " Mammalia of 

 Scotland," and from which I quote, as follows : 



" A consideration of the relative depths of the channels 

 which respectively divide Ireland and the islands from the 

 mainland of Scotland, would lead us to the conclusion that 

 the severance of the former took place first, and that the 

 Orkneys remained longest un-insulated. An upheaval of 

 about 240 to 270 feet would bring the latter again into com- 

 munication with Caithness, while it would require a rise of 

 about 300 to 320 feet to reunite the Hebrides with Skye, and 

 of 700 to 900 feet to restore land communication between 

 the various parts of South- Western Scotland and North- 

 Eastern Ireland. Nor does the distribution of mammal life 

 seem to me to contradict such a hypothesis. The absence 

 from the known fossil fauna of Scotland and Ireland of most 

 of the characteristic post-pliocene English animals shows that 

 the northward migration of these forms was slow, gradually 

 advancing as the glacial conditions of the northern parts of 

 our islands decreased in intensity. Thus it is not difficult 

 to suppose that the hedgehog, small shrew, ermine, badger, 

 squirrel* and mountain hare may have found their way 

 through Southern Scotland into Ireland, long before they 

 were able to penetrate into the still sub-arctic regions of 

 the Highlands. Subsequently, when the continued depres- 

 sion of the land had isolated Ireland, and the improvement 

 of the climate had continued, the shrews and voles may well 



* But compare remarks under Ireland, K. M. Barrington in Proc. Ryl. 

 Dub. Soc, May 1880. 



