The lead is "cast," as the saying goes, "armed" for this emergency. An
iron sinker is made with a hollow recess in the bottom; this is filled
in with tallow, and on striking the bottom any loose matter may adhere
by being pressed into the tallow. If the bottom is rocky or hard we
get simply an imprint in the arming, and when such a result is
obtained the usual construction is that "the bottom is rocky" or hard.

Now, this seems to me a point on which chemistry may give some very
valuable help, for I am convinced that no sounding should be accepted
unless evidence of the bottom itself is obtained. A few considerations
will show that when we are working in very deep water, where there is
a difficulty of knowing for certain that we have an "up and down"
sounding, and the hardening of the "arming" by the cold and pressure,
unless we bring up something we cannot be sure that we have touched
the bottom; leaving the doubt on this point on one side, unless we use
a very heavy sinker, so as to get an indication of the released strain
when it touches the bottom, we encounter another complication.

Sir William Thomson's sounding wire has added the element of
reliability to our soundings in this latter case. The note given out
by the wire when the bottom is reached is perceptibly different when
under strain, even if the dynamometer should give an unreliable
indication.

It has been found that when a "bottom" has been recovered by the
arming with tallow, the adherent grease seriously detracts from the
value of the specimen for scientific purposes. Washing with perfectly
pure bisulphide carbon will save the sounding, but of course any
living organism is destroyed. As we have plenty of contrivances for
bringing up loose "bottoms" without arming, we have nothing to fear on
this score.

There is a great difficulty to explain the vast accumulations of clay
deposits on the ocean bed, and it has been suggested that some minute
organisms may produce these deposits, as others give us carbonate of
lime. Is there not a very great probability of some of the apparently
insoluble rocky formations being answerable for these accumulations?

We must not forget the peculiar changes which such an apparently
stable substance as feldspar undergoes when disintegrated and exposed
to the chemical action of sea water. As these deposits contain both
sodium and potassium, our chemical operations must provide for the
analytical results; in other respec