3-
r ‘.
cavity, we are warranted in supposing that the quantity of oxygen found in
it is larger in deep water than at the surface, owing to that gas being more
essential to vital action, being present in greater abundance, and approaching
more closely to the specific grarity of the surrounding medium than nitrogen.
This riew is borne out, moreover, by the ‘ Bonite ’ analyses, which show the tendency
of the nitrogen to decrease m th the depth.
There is another very remarkable property of gases which demands notice,
although it is impossible, in the present state of our knowledge, to say how far
this property may operate in modifying the combinations of sea-water and its
various ingredients—namely, their liquefaction under great pressure. I t has
been shown that, although the degree of pressure necessary to produce the
liquefaction of a given gas is constant at the same temperature, as the temperature
decreases, so does the amount of pressure requisite to produce the effect
diminish. Amongst the elementai’y gases, chlorine and cyanogen liquefy under
the smallest amount of pressure, and at nearly ordinary temperatures. Oxygen,
on the other hand, which is so refractory as to resist the extreme pressure it
has heretofore been subjected to, when combined with an equal volume of the
vapour of sulphur, as sulphurous-acid gas, becomes liquid at a temperature of
45° Fahr. under a pressure of only two atmospheres. In the same manner
hydrogen, which in its separate state proves equally refractory, on being mixed
with one-third of its volume of nitrogen so as to constitute ammoniacal gas, '
becomes liquid under a pressure of about six and a half atmospheres, at 50° Fahr.;
whilst, by a remarkable change of properties, chlorine, which alone is readily
liquefiable, if united with an equal volume of hydrogen requires a pressure of
forty atmospheres ; and hydrogen and oxygen, both of which gases in their separate
state resist all pressure that has been applied to them, when combined to
form water continue liquid under a pressure considerably below that of a single
atmosphere. Lastly, carbonic-acid gas, which, at a temperature of 32° Fahr.,
requires thirty-six atmospheres to cause it to become liquid, at 14° Fahr. only
requires twenty-seven—a degree of pressure far short of that it is subject to in
the lower zones of the sea.
I t is probable that the saline and mineral substances present in sea-water
exercise a much more marked effect on the formation of the organic deposits of
the deeper zones of the ocean than has been admitted under the antibiotic view
i
so often referred to. From the nature of the difficulties by which the inquiry is
surrounded, not only is the chief portion of our knowledge regarding the deep-
sea bed rather of a theoretical than a practical kind, but, unfortunately, it
must long continue to be so. I t is doubly expedient, therefore, to test this
knowledge by the light of every fact that science or accident may throw in
our way. Thus, notwithstanding all that has been achieved by chemistry and
mineralogy, it still remains an open question whether the great limestone
strata were precipitated from waters holding the mineral in solution, or whether
the separation of the calcareous matter was a vital act involved in the
construction of the shells of creatures holding the lowest rank in the scale
of being. In like manner we are not in a position to state definitely the
manner in which the siliceous concretions of the Chalk and the Carboniferous
limestone were produced. Few persons now-a-days regard the calcareous
deposits as having resulted from chemical, or the siliceous concretions from
mechanical action ; but, although the presence of the shells of the Foraminifera
in immense profusion in some limestones supports the view that the animals to
which they belonged effected the separation in question, there is no such proof
forthcoming in the case of the altered limestones. I f we examine the siliceous
concretions, our perplexities increase rather than diminish ; for whilst remains of
siUceous-sheUed organisms are to be met with in them, it is very remarkable that
they do not belong to the family of siliceous-shelled Ehizopods which, next to
the Foraminifera, are most largely represented at the bed of the ocean, namely,
the Polycystina, and there is no authenticated example, up to the present period,
of a Polycystine shell having been detected in a flint. From the natm-e of the
hydro-silicates, we could hardly expect to find the forms of siliceous organisms
preserved ; hence it is possible that the mineral atoms of the Polycystina have
become merged, as it were, into the substance of the masses. But, since we
constantly detect siliceous spicules of sponges, which have not yielded to dis-
integi-ation though similarly formed, it is difficult to reconcile the apparent anomaly.
I f we regard the concretions as principally made up of sponge-spicules,
the case is but little altered ; for the pseudomorphs of the calcareous shells of
the Foraminifera are plentiful in their substance, and indicate that the conditions
under which they were formed and silicified were such as might have been shared
by the testaceous Rhizopods generally.
K