1904 - 5 .] Study of the Lakes of Scotland and Denmark. 435 
consequently more conspicuous, in Denmark than in Scotland. 
Every year the wide zone of vegetation which surrounds our 
lakes decays in October and November, is broken up by the 
waves, partly pulverised on the shore, and, as detritus, carried 
out over the whole lake ; the vegetation which withstood the 
force of the autumn gales is frozen in the ice, and in spring, 
when the ice breaks up, is scattered over the lake as leaves and 
stems. The lime-crusts, derived from the blue-green Algae 
covering the stones, are peeled off by the action of the ice, and as 
powder carried out from the shore. As stated by Forel (1892-1902), 
Kirchner (1896), myself (1901), and others, the blue-green Algae 
and the fauna living in the Algae-crusts corrode the stones, so that 
the stones become brittle, decay, and are pulverised. Every spring, 
after the first heavy storms, we find the shores strewn with 
thousands of dying snails or empty shells, which are broken up, 
pulverised, and as a tine lime powder, colouring the water in calm 
bays a whitish-grey, are scattered over the lake ; the lime incrusta- 
tions on Potamogeton and other plants will, especially in spring 
and autumn, share the same fate. During these seasons the 
waves reach the bottom in depths of 10 to 15 feet, and the great 
Characea growths, which often cover the bottom, are uprooted, 
cast on to the beach, and undergo the same process of pulverisa- 
tion. The pulverised material remains in suspension in the water 
for a long time, and as detritus affects the transparency of the 
water, — the amount of detritus, especially in spring after heavy 
gales, being very considerable. It may be added, that by no means 
all the material thrown up on the beach is subjected to pulverisa- 
tion, for a larger or smaller proportion is deposited in shallow bays, 
and forming peat, fills them up, and thus diminishes the size of 
the lake. 
The huge masses of plankton will also in the course of time 
reach the bottom. I have shown (1900) that we can often 
detect beneath the layers of living plankton— I think below the 
“ sprungschicht ” — layers of dead plankton, which three or four 
weeks previously had been living plankton in the upper layers of 
water. This dead plankton mostly consists of skeletons, and by 
means of vertical hauls I have followed it on its way to the lake- 
bottom. I have shown, further, that nearly all the protoplasm of 
