THE ORIGIN OF TARNS. 
53 
If not produced by expulsion of matter outwards or sinking 
of matter inwards, these hollows must be the effect of some sur- 
face-working agent. The sea 'planes away along the coast-line, 
and the material goes to fill up ocean hollows ; therefore the sea 
cannot be the agent, and any force in an ocean current is clearly 
out of the question over these scattered spots. Streams and 
rivers work along lines, form ravines and gorges, but never a 
more or less circular basin of great size in comparison with the 
stream, or river ; hence they cannot be the agents. The atmo- 
spheric powers — rain, snow, wind, and chemical action — weather 
the rocks indeed, form tiny basins on almost every stone ; but 
this is but nature’s fretwork, the delicate carving around the 
sculptured craggy tower or spire and smooth-scooped rocky front. 
Yet there is one surface agent remaining, the moving glacier. 
Most people are familiar with the proofs of former glacial action 
in Cumberland and Wales — proofs as clear as are those of the 
former greater extension of the Swiss glaciers. Now by far 
the greater number of our tarns lie in true rock basins — hollows 
completely enclosed by rocky sides, which are, moreover, smoothed 
and grooved in a manner peculiar to ice action. At the sides of 
many a tarn and lake you may see the ice grooves and scratches 
passing beneath the water, so as to leave no doubt whatever that 
ice has once occupied the rocky hollow. The question is, Did 
the ice movement form the hollow ? I believe that in most cases 
it did, and for these reasons : 1 . The tarns lie almost invariably in 
the path of old ice streams or glaciers, as is proved by the direc- 
tion of the scratches in the surrounding rocks. 2. They frequently 
occur at the foot of slopes more or less steep, or where the ice 
pressure can be shown to have been great. 3. The position of 
the deepest points in the larger tarns and lakes occurs almost 
invariably where, from the confluence of two or more glaciers 
or the narrowing of the valley, the ice pressure must have 
been somewhat increased. 4. The depth of these tarns is 
very slight as compared with the thickness of the ice which can 
be proved to have passed over them. 5. There is every grada- 
tion from a tiny rock -bound pool, glaciated on all sides, and 
which all will admit must have been scooped out by the ice, to 
the tarn or lake showing precisely similar phenomena on a larger 
scale. 
Since the ice plough passed over our land the atmospheric 
powers have been at work for a long period, and while many 
rock basins are now completely filled up by stream-borne matter, 
all are being so filled, and each age must witness a decrease in 
the number and size of those sheets of water which form so 
marked a character of our Cumbrian scenery. 
Before quitting this subject, however, I must remark that there 
are a few tarns which seem to me to owe the whole or a part of 
