sition of the deep-sea mud of this intermediate zone is entirely
different from that of the circumpolar regions.

The first exact information respecting the nature of this mud at depths
greater than 1,000 fathoms was given by Ehrenberg, in the account which
he published in the "Monatsberichte" of the Berlin Academy for the year
1853, of the soundings obtained by Lieut. Berryman, of the United States
Navy, in the North Atlantic, between Newfoundland and the Azores.

Observations which confirm those of Ehrenberg in all essential respects
have been made by Professor Bailey, myself, Dr. Wallich, Dr. Carpenter,
and Professor Wyville Thomson, in their earlier cruises; and the
continuation of the _Globigerina_ ooze over the South Pacific has been
proved by the recent work of the _Challenger_, by which it is also shown,
for the first time, that, in passing from the equator to high southern
latitudes, the number and variety of the _Foraminifera_ diminishes, and
even the _Globigerinoe_ become dwarfed. And this result, it will be
observed, is in entire accordance with the fact already mentioned that,
in the sea of Kamschatka, the deep-sea mud was found by Bailey to contain
no calcareous organisms.

Thus, in the whole of the "intermediate zone," the silicious deposit
which is being formed there, as elsewhere, by the accumulation of sponge-
spicula, _Radiolaria_, and Diatoms, is obscured and overpowered by the
immensely greater amount of calcareous sediment, which arises from the
aggregation of the skeletons of dead _Foraminifera_. The similarity of
the deposit, thus composed of a large percentage of carbonate of lime,
and a small percentage of silex, to chalk, regarded merely as a kind of
rock, which was first pointed out by Ehrenberg,[5] is now admitted on all
hands; nor can it be reasonably doubted, that ordinary metamorphic
agencies are competent to convert the "modern chalk" into hard limestone
or even into crystalline marble.

[Footnote 5: The following passages in Ehrenberg's memoir on _The
Organisms in the Chalk which are still living_ (1839), are conclusive:--

"7. The dawning period of the existing living organic creation, if such a
period is distinguishable (which is doubtful), can only be supposed to
have existed on the other side of, and below, the chalk formation; and
thus, either the chalk, with its widespread and thick beds, must enter
into the series of newer formations; or some of the accepted four great
geolog