1904 - 5 .] Study of the Lakes of Scotland and Denmark. 443 
our lakes at 120 feet, while in the certainly much deeper alpine 
lakes they always appear to be dissolved before reaching the 
bottom. I can hardly imagine that the solution in the alpine 
lakes is solely due to the greater depth, because of which the 
deposition would occupy a longer period of time. On becoming 
acquainted with the plankton Diatoms of the Scottish lakes, it 
struck me that the Diatoms in nearly all alpine lakes are the 
thin-shelled Cyclotella , Asterionella , and Fragilaria. Of these 
the two last-mentioned are also common in our lakes, but there 
also their skeletons never produce Diatom-ooze ; in many hundreds 
of samples I have observed very few frustules of these forms, and 
I suppose that in the Danish lakes also they are dissolved before 
sedimentation. The Diatom-ooze in our lakes is produced by 
thick-shelled plankton Diatoms ( Melosira , Stephanodiscus astrcea , 
etc.), species which are rare in the plankton of the alpine lakes, but 
still occurring in the littoral zone. Provisionally, I am inclined 
to believe that the formation of plankton Diatom-ooze in our 
lakes may perhaps be explained by the presence of thick-shelled 
Diatoms in the plankton. The circulation of silicates in the 
lakes is a study of the greatest interest, and one regarding which 
we know very little. 
I think it very probable that a future more exhaustive explora- 
tion will only further prove that the precipitation of organic 
matter derived from the littoral zone and plankton in the Scottish 
lakes is only relatively small. The greater part of the organic 
matter ultimately reaching the bottom in a more or less pulverised 
state is, as far as I can make out, derived from the tops and sides 
of the mountains, carried into the lakes by the rivers. In the 
preceding pages I have made it my object to point out that, 
according to my view r , the organic life in the Scottish lakes , both as 
regards the littoral fauna , the bottom fauna , and the plankton , to a 
very considerable extent likeivise originally belonged to the adjoining 
country , and not to the lake itself. Regarding the deposits on the 
lake- floor, we shall arrive at a similar conclusion. With us it is a 
common rule that the deposits already at about 50 feet mainly 
consist of fine mud, mingled with very few stems, shells, or leaves. 
When dredging at 300 feet in Loch Hess I was greatly surprised 
to find the bottom mainly consisting of very coarse material, mixed 
