248 THE FOREST LANDS OF FINLAND. 
Lakes of each of these kinds may be seen in Scandin-. 
avia and Finland. It is in regard to the formation of the 
last: description of lakes that there is any difficulty, the 
formation of a cup-like hollow in solid rocks, sometimes 
along the line of a valley, sometimes on a plateau, some- 
times on a hill top, or on a watershed. 
There are in many rivers deep holes. At the Cape of 
Good Hope one hears constantly of See-Koo vleys, or hip- 
popotamus holes, and occasionally, even in the rocky bed of 
a river, we find cylindrical cavities called pot-holes. In 
the bottom of such are generally found a-few well-rounded 
pebbles and boulders. The cavities are due to the circular 
movements of these or other stones and boulders, which, 
caught by an eddy, have been kept whirling there, and by 
friction abrading the rock they have gradually formed, 
these holes working downward into the solid rock. And 
often on the sea-shore may be seen cavities lined with 
sea-weed and filled with sea-water, each a natural aqua- 
rium. Some of these are formed, as are the pot-holes, by 
boulders lying in their bottom which have been kept 
whirling round in the eddies of a vexed tideway instead 
of a rapid brook or river. 
But it is not thus that these rock lakes have been formed. 
Of the theory of Professor Ramsay the following illustra- 
tion is supplied by Professor Geikie:—‘A river of ice is 
not bound by the same restraints as those which determine 
the action of a river of water. When a glacier is, as it 
were, choked by the narrowing of its valley, the ice 
actually rises. In such places there is necessarily an 
enormous amount of pressure, the ice is broken into 
yawning crevices, and the solid rocks suffer a propor- 
tionate abrasion, The increased thickness of the mass of 
ice at these points must augment the vertical pressure, 
and give rise to a greater scooping of the bed of the 
glacier. If this state of things lasts, it is plain that a 
hollow or basin will be here ground out of the rock, and 
that once formed, there will always be a tendency to pre- 
serve it during the general lowering of the bottom 
