138 
POPULAR SCIENCE REVIEW. 
the waters of adjoining bays, just as that now in progress 
through the Mont Cenis will connect France with Italy. 
Neither operation is work that shows much advance from 
year to year, but of both the result is sure. Great systems of 
veins, parallel and at light angles to each other, are acted 
upon, and the tunnel creeps on. At the same time, perhaps, a 
little rill of water insidiously makes its way from above, finding 
some means of coming down to the sea below. Very soon 
does the sea take advantage of this slight help. It is the 
mouse gnawing the meshes of the net that holds the lion. A 
part of the ground above falls in, and either a rapid slide of 
part of the cliff, or a gradual and periodical fall of the roof, 
gives the sea something to remove, and supplies fresh hammers 
wherewith to beat at the outer gate. The cavern enlarges as 
the walls and roof recede, — falling to the floor, and removed 
thence by the waves. 
Thus have been formed those magnificent caverns in Sark, 
called “ Les Boutiques/-’ than which few things are finer ; thus, 
also, were formed the “ Gouliot ” caves in the same island. 
The walls of such caverns are generally bare and smooth — 
worn so by the constant trituration of small stones conveyed 
by the sea. They are sometimes also deeply furrowed with 
fissures, not yet expanded. It is only where the tide rises and 
falls many yards that such results are seen on a grand scale ; but 
according to the extent of force exerted, so will be the 
destruction. 
Large caverns that enter far into the land, whose floors were 
originally level with the sea, become by degrees altered in this 
respect, when the roof falls in faster than the sea is able to 
grind up and remove the fragments. Then we often have one 
access to the cavern half-way down a steep face of rock, and 
the floor rises until at last there is a mere open cleft above, and 
no more roof remains to fall. The cavern is then open to 
the sky, and is a kind of natural chimney. The work of the 
sea, however, goes on steadily from below, and at last the fallen 
fragments are removed : the gap or chimney then enlarges, the 
cavern at last ceases to exist, and what was once part of the 
mainland, forming the wall of the cavern seawards, is now a 
rocky islet, soon probably to be removed altogether. 
The picturesque effects seen in the neighbourhood of such 
caverns are numerous and very fine. Detached rocks, pierced 
by natural arches — rocks connected with each other by natural 
flying’-bridges — pinnacles and pyramids of naked rock, looking- 
like huge artificial monoliths — all these are common. Not unfre- 
quently, where circumstances admit, the rocks are clothed above 
with terrestrial green ; below with brown and black marine in- 
crustations of sea-weed, and in the middle they are grey with 
