442 Proceedings of Royal Society of Edinburgh. [sess. 
impressions I formed of the Scottish lakes, I shall next endeavour 
to show how the organic life here also influences the lakes and 
their environs. I have, of course, seen too little of Scotland to 
be able to do so as satisfactorily and exhaustively as I should wish. 
From what I did see, I gathered that, owing to the extreme 
paucity of organic life and the hardness of the soil, as well as the 
lesser amplitude of the variations in the temperature of the 
water, the intensity of all those processes due to the influence of 
organic life is much less marked than in the Danish lakes. 
As a zone of higher vegetation in the larger Highland lakes is 
almost entirely wanting, peat formation along the shores is almost 
out of the question ; only a very small amount of organic material 
from the shores is scattered over the lakes, in the form of 
detritus, diminishing the transparency of the water. The stones, 
as far as I am aware, are never covered with lime-incrustations 
derived from blue-green Algae ; the Potamogetons, etc., are never 
seen covered with lime-crusts ; and the shells of mussels or snails 
never abound in such quantities on the beach that their pulverised 
fragments, in the shape of lime-powder, are scattered over the 
lakes, or influence the percentage of lime in the water or in the 
deposits on the lake-floor. The amount of plankton in the larger 
Highland lakes is never or very rarely so great as to affect the 
colour of the water in any notable degree ; most probably it may 
affect, to a relatively slight extent, the transparency, and the 
amount and quality of the air in the water. 
From my studies of the deposits in Loch Hess, Loch Oich, and 
Loch Lochy, I suppose that the precipitation of decayed or 
decaying matter derived from the plankton is very insignificant. 
Of course, I never found any great quantities of blue-green mud 
derived from blue-green plankton Algae, but even the chitinous 
valves of Daphnids are rare. In Loch Lochy, at a depth of 500 
feet, I most frequently found the carapaces with long antennae of 
Bosmina. A most remarkable and interesting thing is that the 
frustules of Diatoms, as in the Swiss lakes, are comparatively 
rare, and the skeletons that do occur are, to my knowledge, only 
those of bottom and shore Diatoms, the plankton Diatoms being 
almost entirely absent. It has long been an enigma to me wdiy 
the skeletons of the plankton Diatoms accumulate on the bottom in 
