74 
HINTS TO TRAVELLERS. 
care must be taken not to mistake glacier valleys, such as the friths and 
lochs of Scotland, and the fiords of Norway, for valleys of subaerial erosion 
that have recently undergone subsidence. It is highly probable, even in 
this case, that the valleys were originally formed by fresh-water denuda¬ 
tion, and that they have been depressed, but their features have been 
modified by the action of ice. 
Rivers and River-Plains .—At the present time a question of much 
interest is the antiquity of existing land-areas, and some light may be 
thrown upon this, if the relations of existing river-basins to those of past 
times can be determined. If a stream cuts its way through a high range, 
it is probable that the stream is of greater antiquity than the range, and 
either once ran at an elevation higher than the crest of the ridge now 
traversed, or else has cut its way through the range gradually during the 
slow elevation of the latter. Where a river traverses a great alluvial 
plain, it may fairly be inferred that a long time has been occupied in the 
accumulation of the deposits to form the plain; but it remains to be seen 
whether those deposits are not partly marine or lacustrine. If upheaval 
has taken place over any portion of the plain, or if the river has cut its 
bed deeper, sections may be exposed, and these should always be ex¬ 
amined for fossil remains. Bones of extinct animals are not unfrequently 
found in such deposits. 
Lakes .—The mode of origin of lakes is always a subject of considerable 
geological interest. Some lakes occupy areas of depression; others 
valleys of erosion, the drainage from which has been stopped by local 
elevation, by land-slips, or by deposits from tributaries, whilst very 
many, and amongst them some of great size and depth, occur in 
regions that have been covered by ice; and it is still a moot point 
how far these lakes are due to partial changes in the elevation of 
the country, some observers having adopted, while many others dispute 
the views of the late Sir A. Ramsay, who believed all these hollows to 
have been scooped out by ice moving over the surface in the form of 
a glacier or of an ice-sheet. Of the smaller lakes, some are dammed 
up by landslips, some by glacial moraines, and a few occupy volcanic 
craters. 
Evidence of Glacial Action .—Closely connected with the subject of 
lakes is that of glacial evidence generally. There is probably no geo¬ 
logical question which has produced more speculation of late years than 
