Plain men may be puzzled to understand why Dr. Wyville Thomson, not being
a cynic, should relegate the "Land of Promise" to the bottom of the deep
sea, they may still more wonder what manner of "milk and honey" the
_Challenger_ expects to find; and their perplexity may well rise to its
maximum, when they seek to divine the manner in which that milk and honey
are to be got out of so inaccessible a Canaan. I will, therefore,
endeavour to give some answer to these questions in an order the reverse
of that in which I have stated them.

Apart from hooks, and lines, and ordinary nets, fishermen have, from time
immemorial, made use of two kinds of implements for getting at sea-
creatures which live beyond tide-marks--these are the "dredge" and the
"trawl." The dredge is used by oyster-fishermen. Imagine a large bag, the
mouth of which has the shape of an elongated parallelogram, and is
fastened to an iron frame of the same shape, the two long sides of this
rim being fashioned into scrapers. Chains attach the ends of the frame to
a stout rope, so that when the bag is dragged along by the rope the edge
of one of the scrapers rests on the ground, and scrapes whatever it
touches into the bag. The oyster-dredger takes one of these machines in
his boat, and when he has reached the oyster-bed the dredge is tossed
overboard; as soon as it has sunk to the bottom the rope is paid out
sufficiently to prevent it from pulling the dredge directly upwards, and
is then made fast while the boat goes ahead. The dredge is thus dragged
along and scrapes oysters and other sea-animals and plants, stones, and
mud into the bag. When the dredger judges it to be full he hauls it up,
picks out the oysters, throws the rest overboard, and begins again.

Dredging in shallow water, say ten to twenty fathoms, is an easy
operation enough; but the deeper the dredger goes, the heavier must be
his vessel, and the stouter his tackle, while the operation of hauling up