410 Proceedings of Royal Society of Edinburgh. [sess. 
expect from the observations in other alpine lakes. As regards 
the transparency, there is still this great difference between the 
lakes of the two countries — that in the Danish lakes the trans- 
parency is always and everywhere greatest in spring, and slowly 
diminishes with increasing temperature, whereas in the Scottish 
lakes, according to my informants, the transparency is nearly 
constant all the year round, hut may at any season, especially 
after heavy rains, be suddenly greatly reduced. 
As to the colour of the water, another great difference between 
Danish and Scottish lakes is to be noted ; for while the colour of 
our lakes undergoes a regular alternation, strictly dependent on the 
different seasons, the colour of the Scottish lakes varies very 
little at all seasons. The larger Scottish lakes never show that 
turbid yellowish-green colour so characteristic of nearly all our 
lakes from May to November, nor the deep blue colour displayed 
by our lakes in April, neither are they covered with “wasserbluthe” 
caused by blue-green Algse. The water in all the Scottish lakes 
seems to he very clear, hut has a yellowish-brown colour, quite dif- 
ferent from the blue colour of most of the alpine lakes in Switzer- 
land, which are also characterised by the great transparency of the 
water : in both the Swiss and Danish lakes the transparency is 
much greater in winter and spring than in summer and autumn. 
As will be noted in a later chapter, the colouring of the Danish 
waters is due to the plankton ; the colouring of the Scottish lakes 
has quite a different origin. It must he remembered that the 
Scottish rivers nearly always drain through peaty hogs and the 
moss-covered sloping sides of the mountains, and only very 
rarely, and for a short period of the year, do the rivers obtain 
their water directly from the snow. 1 am told that the layer of 
peat on the mountains may attain a thickness of 1 to 2 feet, 
and it will therefore he easily understood that the water of the 
Scottish lakes must necessarily he peaty and very rich in humic 
acid, and this fact accounts for their yellow-brown colour and very 
slight transparency. In my opinion we have here the most strik- 
ing and the most interesting difference between the alpine lakes of 
Switzerland, with their clear blue water, their rivers fed directly 
from the vast eternal glaciers, and the alpine lakes of Scotland, with 
their yellowish-brown water, their rivers rising in bogs and travel’s- 
