WHITE CHALK COMPARED WITH CALCAREOUS OOZE. 537 
calcareous oozes. The more delicate shells in the surface layer 
must be the first to yield to this influence and must help to form 
the fine calcareous powder or paste in which the stronger shells 
are embedded. Thus we might naturally expect that this disin¬ 
tegration of the more friable shells would continue even after a 
given layer was covered by several inches of fresh deposit, and 
consequently that the aspect of the material in its lower layers 
would be very different from that of its surface layer. 
As a matter of fact, the sounding tube of the Challenger apparatus 
did on a few occasions pierce the surface layer and brought up 
samples of just such a more compact deeper layer as might have 
been expected. Perhaps the most remarkable case of this was 
at Station 334 in the South Atlantic, at a depth of 1,915 fathoms, 
and is thus described (Op. cit., p. 143): “ The sounding tube 
had sunk about a foot (30 cm.) into the bottom and brought 
up a litre of the deposit. Of this there were two layers, separated 
by a thin dark line, an upper layer of a light brown colour and 
about 8 inches (20 cm.) in thickness ; and a lower, milk-white 
and over an inch in thickness, chiefly made up of amorphous 
calcareous matter and coccoliths. On analysis the upper layer 
gave 84*65 per cent, of carbonate of lime, the lower 85*7? per cent.” 
Again, at Station 331, in the same region and at a depth of 
1,715 fathoms, “the tube had sunk a foot into the bottom and 
brought up about a quart (over a litre) of the ooze. The lower 
layers were more compact than the upper” (Op. cit., p. 141).* 
Differences between the top and the lower layers were noticed 
also at Station 270 (Pacific), Station 283 (Pacific), Station 296 
(Pacific), and Station 330 (Atlantic). 
I believe M. A. de Grossouvre was the first to point out the 
significance of these facts. Writing in 1892 f on the conditions 
under which chalk has been formed, and admitting the differ¬ 
ence between chalk and Globigerina ooze taken from the surface 
layer, he remarks, “ in this connection, however, we should take 
note of the results of certain soundings, which have shown that, 
while the surface layer of the Globigerina ooze was formed princi¬ 
pally of the shells and shell-debris of these organisms, the sub¬ 
jacent layer consisted solely of very fine calcareous mud, as if 
the Globigerina were perfect only in the upper layer and those 
underneath had crumbled into dust in consequence of the de¬ 
composition of the organic matter ” [in their shells]. 
The probability of such a difference between the upper and 
lower layers of Globigerina ooze was independently pointed out 
by Professor J . B. Harrison and myself in 1895J when comparing 
some specimens of the modern ooze with Tertiary and Cretaceous 
* Wyville Thomson (Depths of the Sea, p. 409) has carefully described a 
dredging obtained in 1869 from the Bay of Biscay, in which the lower part 
consisted mainly of compact structureless chalky mud, markedly contrasting 
with the surface layer of Globigerina ooze. 
+ Ann. Soc. Geol. Nord, Vol. xx. p. 7. 
7 Quart. Journ. Geol. Soc., Vol. li., p. 328, 
