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POPULAR SCIENCE REVIEW. 
yearly waste of mountain side and the matter brought down by 
every stream have filled up many a mountain pool, and frequent 
peat mosses mark the spot where once the waters danced in the 
mountain breeze. Whence these hollows ? What is their 
origin ? Do we see in them the relics of volcanic effort ? Are 
the combs (cwm), coves, or corries in which they lie the vestiges 
of volcanic craters, as the form of many at first, perhaps, suggests ? 
Or have we here hollows produced directly by surface action ? 
Again, are these hollows of great depth, or are they shallow ? 
What is their general form ? Now, there is little doubt 
that most people, if asked to draw the form of the hollow in 
which the waters of a tarn now lie so placidly, would grossly 
exaggerate its true depth, or, perhaps, liken it to the basin formed 
by placing the two hands together, side by side, curved, with the 
palms uppermost. Some years since I took a number of sound- 
ings among the Cumbrian lakes and tarns, and communicated 
the results of my examination to the Geological Society (Quart, 
Journ. Geol. Soc. vol. xxx. p. 96, and vol. xxxi. p. 152). Hold 
out one hand, palm uppermost, and straighten it as much as 
possible — the hollow in the palm is yet far too deep to represent 
with truth the natural rock basin. Soundings taken in lakes 
throughout the district all show the same thing — the basins are 
very shallow compared with their size and the height of the 
surrounding hills. 
Next, let us search out the origin of these shallow basins. 
At the outset we distinguish two classes of action, one of which 
must have been at work. Either the matter formerly filling the 
hollow has been dug out and carried away by some agent work- 
ing at the surface ; or force from below has here sought a 
vent, and dispersed the matter far and wide ; or, from failing 
support, the ground has sunk at this spot into a hollow. 
First we will consider the upward or downward theory. If 
these numerous mountain hollows with included tarns be of 
volcanic origin, then it is clear we shall find the signs of a 
crateral hollow such as we see them in many parts of the world 
at the present day. There are no such signs. It is true that 
in many cases the surrounding rocks are of volcanic origin ; but 
the volcanic beds, in their lie and position, show no manner of 
relation to the tarn hollows ; and a little study of the rocks of the 
district and the form of the ground clearly shows that the 
volcanoes which gave rise to the ashes and lavas forming many 
of Cumbria’s highest mountains, were active, not as but yester- 
day, but in untold ages past. Then, as to the downward or 
special depression theory, when we can conceive such minute 
subsidences taking place at a great number of almost micro- 
scopic spots without affecting the rocks around, or leaving any 
evidence of a sinking away, we may admit it as possible. 
