il/r Harvw-Broion on the Squirrel in Great Britain. 165 



of Stirling ; so that bridges, roads, rails, and " dykes " may be 

 considered as great aids in the extension of their range.* 



This concludes my account of the extension of range of 

 the squirrel throughout Scotland, and it will be observed 

 that I have treated the subject on a plan almost uniform 

 with my account of the Capercaillie in Scotland.-f- I would 

 have preferred to indicate upon the map accompanying this 

 portion, the dates of the " steps of advance," as I have done 

 in the map of the Caj^ercaillie, but the scale of this map 

 scarcely admits of a sufficiently minute treatment in this way. 



GENERAL REMARKS ON THE LAWS REGULATING THE EXTENSION 

 OF RANGE OF THE SPECIES. 



It has been pointed out in the foregoing pages, First, 

 The localities where the squirrel is supposed to have become 

 extinct, where it lingered longest before it became extinct, 

 and those where it lingered and revived again ; and. Second, 

 The lines of advance, and the areas at present occupied by the 

 species. The history of the species is almost identical with 

 that of many others whose natural habitat is a forest-clad 

 country. It is found to have lingered longest where the 

 forest remained longest, and to have revived most rapidly (or 

 spread most rapidly after restoration) where forest trees had 

 been planted. The lines of their advance have been in- 

 fluenced principally by the various barren chains of moun- 

 tains adverse to their conditions of life, and by the growth 

 and increase of wood, favourable to their increase and exten- 

 sion of range. AVhere trees have lingered, amidst the Highland 

 glens, they lingered too ; and where trees have led them of 

 late years they have reached considerable altitudes. " The 

 recesses of the Highlands have ever proved the shelter and 

 protection of the descendants of the older tribes of the 

 country, and the limit to the advance of a stranger popula- 

 tion." These words, applied to the human races that in- 

 habited the several kingdoms of "Ancient Alban," are 

 equally applicable to many races of animals which have 



* And see also under General Remarks on Extension of Range, infra. 

 t David Douslas, Edinburgh. 



