by such cuiTcnts. Lastly, inasmuch as the shells of GloMgerina surpass in massiveness
and density those of any of the other minute structures met with in the
deep-sea deposits, excepting the Polycystina—if we assume the deposits to be
formed by the gradual subsidence of organic atoms from the transporting currents,
it follows that the proportion of light forms to heavy ones would invariably be
the greatest at the greatest distances from land,—a result which is not in accordance
with observation.
The extreme lightness of some Foraminiferous deposits has been alluded to by
Captain Maury, in his admirable work on the ‘ Physical Geography of the Sea,’
as “ suggesting the idea that the sea, like the snow-cloud with its flakes in a
calm, is always letting fall upon its bed showers of these microscopic shells ; ’ ’
and he adds, “ the ocean, especially within and near the tropics, swarms with
life ; the remains of its myriads of moving things are conveyed by currents,
and scattered and lodged in the course of time all over its bottom ; this process,
continuing for ages, has covered the depths as with a mantle, consisting of organisms
as delicate as the macled frost, and as light as the undrifted snow-flake on
the mountain ” *.
This flocculent character is distinctly observable on the immediate surface-layer
of all deposits, and in a few cases, in which the quantity of extremely fine amorphous
particles is excessive, it extends to some depth. Such is the condition
observable in those localities where the Foraminifera are either absent or constitute
the smallest percentage of the material. But in the majority of the deposits,
the flocculence does not extend beyond half an inch or an inch below the
surface, and it is then replaced by a stratum of the utmost tenacity. This marks
the limit of the amorphous non-mineral particles, and the point at which the
consolidation of the heavier atoms commences. Although satisfied of the correctness
of that portion of Captain Maury’s statement which describes “ the remains
of myriads of moving things as being conveyed by currents, and scattered and
lodged in the course of time all over ” the sea-bottom, I am unable to confirm
by my own experience either in the North or South Atlantic that portion of it
which relates to “ showers of microscopic ” (Foraminiferous) “ shells.” Free-
floating Foraminifera are undoubtedly to be met with on the surface of the ocean,
as well as free-floating Polycystina, Diatomacese, and other less known and
* ‘ Physical Geography of the Sea,’ by Captain Maury. London, 1858 : p. 265.
i
common organisms ; but these never constitute the bulk of the deep-sea deposits,
as Glohigerina does. They live within reach of the surface, and are more frequently
to be seen in tropical regions ; but there is good ground for the belief
that the amount of minute animal and vegetable life in tropical and extra-tropical
latitudes is far more evenly balanced than has generally been supposed, and that
the preponderance to which Captain Maury and other obseiTers have drawn
attention as characteristic of the tropics is dependent, not so much on the
superabundance of forms within the tropics, as on the rarity of those favourable
atmospheric conditions upon which the presence at the immediate surface of extra-
tropical forms depends *.
Some of the Globigerina-deposits are of great purity ; but I have reason to
believe I originally overestimated the percentage of shells and debris, and that
the singular absence of amorphous particles in the two specimens on which my
estimate was based was due to percolation of water through the mass of the
material dui'ing its progress from the bottom to the surface. The average proportion
of shells varies from 70 to 85 per cent., the remainder consisting of
amorphous particles and variable quantities of mineral matter, Polycystina, Diatomace
®, Sponge-spicules, and not nnfrequently fragments of Echinoderm structure.
Turning from the shell, which, in this as in the other Foraminifera, furnishes
no characters distinctive of vitality, and, in the majority of the species, does not
even enable us to pronounce whether they are recent or fossil, we find that there
is nothing either in the quantity, the colour, the consistence, or the optical appearances
of the soft parts to indicate that the Glohigerince of the pui-e deposits
do not live where they are discovered. From the difference in colour between
the surface-layer of the deposits and the mass beneath, and also owing to the
extreme tenacity of the inferior stratum, it appears probable that the Ihing Glo-
bigerince are altogether confined to the former,—this view receiving additional
support from the fact that the aspect of specimens taken from the surface corresponds
with that of shells known to be alive, whereas the dingy look of those
from the subjacent stratum corresponds with that of shells known to be dead.
In one case the colour is a vivid but light burnt sienna, the fleshy matter viscid
* The observations of Dr. Joseph Hooker in the Antarctic Sea tend rather to prove a superabimdance
of the minute organic forms in its waters.
T 2