cavities and finest tubes
in the Foraminifer were sornetilnes reproduced in solid counterparts of
the glassy mineral, while the calcareous original had been entirely
dissolved away.

Contemporaneously with these observations, the indefatigable Ehrenberg
had discovered that the "greensands" of the geologist were largely made
up of casts of a similar character, and proved the existence of
_Foraminifera_ at a very ancient geological epoch, by discovering such
casts in a greensand of Lower Silurian age, which occurs near St.
Petersburg.

Subsequently, Messrs. Parker and Jones discovered similar casts in
process of formation, the original shell not having disappeared, in
specimens of the sea-bottom of the Australian seas, brought home by the
late Professor Jukes. And the _Challenger_ has observed a deposit of a
similar character in the course of the Agulhas current, near the Cape of
Good Hope, and in some other localities not yet defined.

It would appear that this infiltration of _Foraminifera_ shells with
_Glauconite_ does not take place at great depths, but rather in what may
be termed a sublittoral region, ranging from a hundred to three hundred
fathoms. It cannot be ascribed to any local cause, for it takes place,
not only over large areas in the Gulf of Mexico and the Coast of Florida,
but in the South Atlantic and in the Pacific. But what are the conditions
which determine its occurrence, and whence the silex, the iron, and the
alumina (with perhaps potash and some other ingredients in small
quantity) of which the _Glauconite_ is composed, proceed, is a point on
which no light has yet been thrown. For the present we must be content
with the fact that, in certain areas of the "intermediate zone,"
greensand is replacing and representing the primitively calcareo-
silicious ooze.

The investigation of the deposits which are now being formed in the basin
of the Mediterranean, by the late Professor Edward Forbes, by Professor
Williamson and more recently by Dr. Carpenter, and a comparison of the
results thus obtained with what is known of the surface fauna, have
brought to light the remarkable fact, that while the surface and the
shallows abound with _Foraminifera_ and other calcareous shelled
organisms, the indications of life become scanty at depths beyond 500 or
600 fathoms, while almost all traces of it disappear at greater depths,
and at 1,000 to 2,000 fathoms the bottom is covered with a fine clay.

Dr. Carpente