Indian Islands, at depths from five to fifteen fathoms, becomes
discoloured, and even the anchors of vessels have been moved. ("Journal of
Royal Geographical Society" volume 5 page 25. It appears from Mr. Scott
Russell's investigations (see Mr. Murchison's "Anniversary Address
Geological Society" 1843 page 40), that in waves of translation the motion
of the particles of water is nearly as great at the bottom as at the top.)
There are, however, some difficulties in understanding how the sea can
transport pebbles lying at the bottom, for, from experiments instituted on
the power of running water, it would appear that the currents of the sea
have not sufficient velocity to move stones of even moderate size:
moreover, I have repeatedly found in the most exposed situations that the
pebbles which lie at the bottom are encrusted with full-grown living
corallines, furnished with the most delicate, yet unbroken spines: for
instance, in ten fathoms water off the mouth of the Santa Cruz, many
pebbles, under half an inch in diameter, were thus coated with Flustracean
zoophytes. (A pebble, one and a half inch square and half an inch thick,
was given me, dredged up from twenty-seven fathoms depth off the western
end of the Falkland Islands, where the sea is remarkably stormy, and
subject to violent tides. This pebble was encrusted on all sides by a
delicate living coralline. I have seen many pebbles from depths between
forty and seventy fathoms thus encrusted; one from the latter depth off
Cape Horn.) Hence we must conclude that these pebbles are not often
violently disturbed: it should, however, be borne in mind that the growth
of corallines is rapid. The view, propounded by Professor Playfair, will, I
believe, explain this apparent difficulty,--namely, that from the
undulations of the sea TENDING to lift up and down pebbles or other loose
bodies at the bottom, such are liable, when thus quite or partially raised,
to be moved even by a very small force, a little onwards. We can thus
understand how oceanic or tidal currents of no great strength, or that
recoil movement of the bottom-water near the land, called by sailors the