Pvn H,i I'UitlS

VI INTRODUCTION.
overlooked, unless they advance some startling proposition
as to the origin or remote antiquity of our own
race. There can be no use, however, in blaming the
popular taste ;
nor would it be reasonable to expect that
every one should follow a scientific path, if his inclinations
do not lead him that way. The love of Nature
is not confined to any one period, and its votaries must
not feel disappointed, should their peculiar studies not
be shared by all their contemporaries.
Before entering into the details of our marine Mol-
lusca,
I would make a few more remarks as to their
distribution and structure. This I was prevented from
doing in the introductory part of the former volume by
an anxiety not to impose too long an exordium on the
patience of my readers.
The sea-bed may be said, in the technical language of
lawyers, to be u land covered with water." Its outline,
if it could be viewed through an aquatic telescope, would
be seen to be irregular, and nearly as much diversified
as the surface of the earth. Mountains, hills, rocks,
gorges, valleys, and plains would be successively exhibited
in the submarine panorama, having often the same
bold and abrupt contour that gives so picturesque an
aspect to land scenery. Oceanic and tidal currents
represent rivers, corresponding with them in volume and
rapidity, and equally scooping
degrees of width and depth.
out channels of various
But we have good reason
to believe that lifeless deserts, like the great Sahara, are
wanting below the broad watery girdle which encircles
the globe and covers at least three-fourths of its extent.
It is true that, in certain inlets or arms of the sea, rivers
flowing into them may have sufficient strength and
velocity to sweep the middle of the channel, and thus
prevent the deposit
of mud or other sediment which