64 
POPULAR SCIENCE REVIEW. 
formation of lakes, and it is well to be cautious, in studying* the 
origin of lake-basins, to bear in mind the many and complicated 
causes to which they may be due. 
These questions belong to the minor features in our scenery. 
They have been produced by many local causes, and it is im- 
possible here to treat of them in any but a general way. 
The influence of glaciers, which are well known to have 
existed on the high grounds of Wales and in the lake district, 
has been spoken of, and some of the valleys have been con- 
siderably modified, if not to a great extent formed by them. 
In limestone districts, as in Derbyshire and Somersetshire, 
the power of rain-water holding carbonic acid is very great in 
dissolving the rock and forming caverns, and sometimes, when 
the conditions are favourable, re-depositing the carbonate of 
lime in the form of stalactites or stalagmites ; or, again, form- 
ing a petrifying spring and encrusting leaves, shells, and other 
objects with a deposit of tufa. It has been supposed that some 
of the dales and ravines may originally have been caverns. Be 
this as it may, the action is the same — these limestone combes 
and dales have been formed by running water, assisted, no 
doubt, by the mechanical action of frost, and the chemical 
action of carbonated water. 
We may here also call attention to what is really a very 
minor point in connection with scenery, but which yet has 
many points of interest in connection with physical geography. 
The origin of certain small holes and excavations in lime- 
stone rocks has given rise to much discussion. The atmosphere, 
pholades, and land snails have severally been called into account 
for them, and from the observations that have been made, there 
seems to remain little doubt that all three agents share in 
boring and burrowing into rocks. By far the larger number of 
holes and irregular cavities on limestone rocks are undoubtedly 
due to atmospheric wear and tear, but there are certain small 
holes more or less regular in shape, about which discussion has 
taken place. Some are, doubtless, bored by pholas, which can 
pierce almost any rock, but these burrows are of a pear-shaped 
or pyriform character, and need hardly be mistaken, although 
there is no reason to doubt that the atmosphere could mimic 
these forms, so varied are the shapes it has fashioned. There 
are other holes, unlike pholas-burrows, and occurring in situa- 
tions where it would seem that meteoric agencies had no play, 
which have been attributed by the Bev. T. Gr. Bonney and Mr. 
J. Rofe to the action of our common land-snails. 
Long ago Dr. Buckland, and subsequently M. Bouchard- 
Chantereaux, advocated the boring powers of snails, but their 
views appear to have met with little credence. Mr. Rofe argues 
very ably for snail-action. The odontophore of the gasteropods, 
