62 Proceedings of the Royal Physical Society. 



the destruction of forests ; * in others — and this, I believe, to 

 be the most general — to a combination of these factors. Two 

 of these may be best expressed by quoting the following pas- 

 sage in Murray's " Distribution of Mammals : " " If man or 

 carnivorous animals were amongst them, their extinction 

 would only be the more rapid. If none but herbivorous 

 animals took refuge there, the food would be insufficient for 

 numbers, and they would drop off by inanition." The 

 scarcity of food might be occasioned by the great age of the 

 forests, or by destruction of forests either by fire or by cut- 

 ting down ; and another factor, working in unison with these, 

 may have been the severity of the winters as hinted at by 

 one of my correspondents. The super-abundance also of 

 carnivorous animals would hasten their extinction. 



Nor can we account for the curious migratory habits of 

 many species, — more especially noticeable in virgin forests, 

 but also distinctly and constantly brought before our notice 

 even in this country at the present day, — otherwise than by 

 applying the well-known natural law, which enforces a 

 natural extension of species. I do not speak of the seasonal 

 migrations of birds which pass along our shores, halting only 

 to rest for a brief period ere they resume their long flights to 

 and from the far north ; but of the local migrations, which, 

 if we may use the phrase, sway backwards and forwards 

 from one part of a limited area to another, and are occasioned 

 by, and regulated by, the food supply or the capabilities of a 

 district. If these safety valves were closed, the consequence 

 would be poverty of blood, starvation, disease, helplessness 

 before a natural foe, death, annihilation ; and much goes to 

 prove the unfavourable general character of the comparatively 

 limited area of North Britain at the time of the decline of 

 the squirrel, and the extinction of the Capercaillie and other 

 animals. We have seen that, at least in Strathspey, the 



* It was the custom to fell trees in ancient times for several reasons : when 

 the farm-houses were built on the hill slopes the valleys were great forests, 

 and the people burned great portions to rid them of wolves, and lest enemies 

 should also find shelter. Later, when the country became more peaceful, 

 the inhabitants descended to the valleys and destroyed the forests, in order 

 to make clearings for agricultural purposes, and on which to build their 

 houses. 



