46 (July, 
tion decidedly more exciting than pleasant. At about 800 feet the 
trees become less frequent (except beside the burns), and the heather 
and Wyrica more exuberant, but becoming less so as we reach a height 
of 2000 feet, at which beds of dwarf birch (Betula nana), cloud-berry 
(Rubus chamemorus), and other alpine plants appear. Here, too, is a 
small deep loch (producing Dytiszus lapponicus, &c.), whose waters and 
banks were inhabited by several boreal insects. 
In recording the results of my investigations of the Lepidoptera of - 
Rannoch and Achilty, I mentioned all (or nearly all) the species met 
with, and by comparing these lists with the list of what I found in 
Strathglass, and with lists of the productions of other parts of the 
Highlands, I am led to the conclusion that, given the requisite amount 
of uncultivated ground and of natural wood, the fauna of nearly every 
part of the Highlands (especially north of the Grampians) will be 
found almost identical, and only modified in four respects, viz. : 
lst—By the altitude of the mountains ; 
2nd—By the proximity of the sea ; 
3rd—By the apparently local situation of a few species, the cause 
of which is obscure ;* 
4th—By the longitude. 
1. Of truly alpine Macro-Lepidoptera (i. e. species not found below 
a certain altitude) we have only about 8 or 10 species in Britain ; and 
though many of these are at present known to have but few localities, 
it is probable that when all the lofty mountaims have been examined, 
their range will be found to be co-extensive with the required altitude. 
It is natural to suppose that as we go north we should gradually find 
the necessary altitude (in Britain) becoming less and less; but in 
northern Scotland we are limited to so comparatively small an area, 
that it would require very careful observations to establish this. If, 
however, we were to take the case of a species common to the Alps, to 
the Scottish mountains, and to the Scandinavian fauna, and to carefully 
note the altitudes at which it was found as we proceeded towards the 
north, we would obtain a series of heights beginning at several thousand 
feet above the sea, and gradually descending to the sea level. 
2. I have referred to the influence of the sea in a previous note 
(Vol. vi, p. 170), and several instances of this influence will be found in 
Mr. Norman’s lists of the Forres Lepidoptera. 
3. The local distribution of some few species will probably, when 
* ** Who can explain why one species ranges widely and is very numerous, and why another allied 
species has a narrow range and is rare ?’"—Darwin, “ Origin of species,” p. 5. 
