26 THE FOREST LANDS OF FINLAND. 
fort. High above the bed of the present rapids immense 
caverns have been hollowed in the adjoining rock, indica- 
tive of the tunnelling of the river in byegone times. At 
a distance of about fifteen miles below. Lake Saima the 
Wuoksi is navigable. Before falling into Lake Ladoga at 
Kexholm it spreads out into two large lakes, but through- 
out the greater part of its length, according to Murray, it 
winds between high banks formed of granite, with layers 
of clay and sand, The total length of the river is 170 
versts, 113 miles. Geological data prove that the river is 
decreasing in volume, the ancient breadth of its course 
being in many places marked by round, kettle-shaped 
holes, in which boulders no longer gyrate. The limits of 
the old bed may be clearly seen in the vicinity of the 
Falls. 
The Falls of Wallin-Koski and Kiiri-Koski, a short 
distance beyond those of Imatra, are inferior in grandeur, 
but ‘far more picturesque. The Falls of Imatra may be 
taken as a type of many of the waterfalls met with in 
Finland, in Sweden, in Norway, and in the same latitudes 
in Russia. 
It is easy to imagine the phenomena accompanying the 
gradual advance of a waterfall upwards in the water course 
of a river. In many books on geology the process is 
described. To meet a popular opinion that rivers flowing 
through ravines found these ravines existing as rents in the 
-mountain chain, and availed themselves of them to escape 
to a lower level, Professor Geikie has given in a volume 
entitled “The Scenery of Scotland, viewed in connection 
with its Physical Geology ”—a volume I may afterwards 
have occasion to cite at greater Jength—a graphic account 
(p. 18-34) of the action of a river in forming for itself a bed 
and a valley in which this bed seems to lie at rest, More 
briefly, the action of a waterfall may be described thus: 
Where the current below the fall is not so strong as to roll 
away the fallen rocks, where it is such as to sap the 
