of the mode of origin of this singular deposit
of red clay.

I cannot say that the theory put forward tentatively, and with much
reservation by Professor Thomson, that the calcareous matter is dissolved
out by the relatively fresh water of the deep currents from the Antarctic
regions, appears satisfactory to me. Nor do I see my way to the
acceptance of the suggestion of Dr. Carpenter, that the red clay is the
result of the decomposition of previously-formed greensand. At present
there is no evidence that greensand casts are ever formed at great
depths; nor has it been proved that _Glauconite_ is decomposable by the
agency of water and carbonic acid.

I think it probable that we shall have to wait some time for a sufficient
explanation of the origin of the abyssal red clay, no less than for that
of the sublittoral greensand in the intermediate zone. But the importance
of the establishment of the fact that these various deposits are being
formed in the ocean, at the present day, remains the same; whether its
_rationale_ be understood or not.

For, suppose the globe to be evenly covered with sea, to a depth say of a
thousand fathoms--then, whatever might be the mineral matter composing
the sea-bottom, little or no deposit would be formed upon it, the
abrading and denuding action of water, at such a depth, being exceedingly
slight.

Next, imagine sponges, _Radiolaria, Foraminifera_, and diatomaceous
plants, such as those which now exist in the deep-sea, to be introduced:
they would be distributed according to the same laws as at present, the
sponges (and possibly some of the _Foraminifera_), covering the bottom,
while other _Foraminifera_, with the _Radiolaria_ and _Diatomacea_, would
increase and multiply in the surface waters. In accordance with the
existing state of things, the _Radiolaria_ and Diatoms would have a
universal distribution, the latter gathering most thickly in the polar
regions, while the _Foraminifera_ would be largely, if not exclusively,
confined to the intermediate zone; and, as a consequence of this
distribution, a bed of "chalk" would begin to form in the intermediate
zone, while caps of silicious rock would accumulate on the circumpolar
regions.

Suppose, further, that a part of the intermediate area were raised to
within two or three hundred fathoms of the surface--for anything that we
know to the contrary, the change of level might determine the
substitution of greensand for the "chalk"; whi