Sea-bottom procured by H.M.S. ‘Challenger’ 293 
covering large areas in the Atlantic, and met with also between 
Kerguelen’s Island and Melbourne. Into this red clay he describes 
the Globigerina-ooze as graduating through the “ grey ooze ;” 
and he affirms this transition to be essentially dependent on the 
depth of the bottom. ““ Crossing,” he says, ‘‘ from these shallower 
regions occupied by the ooze into deeper soundings, we find univer- 
sally that the calcareous formation gradually passes into, and is 
replaced by, an extremely pure clay, which occupies, speaking 
generally, all depths below 2500 fathoms, and consists almost en- 
tirely of a silicate of the red oxide of iron and alumina. .....~ 
The mean maximum depth at which the Globigerina-ooze occurs 
may be taken at about 2250 fathoms; the mean depth at which 
we find the transition grey ooze is 2400 fathoms ; and the mean 
depth of the red-clay soundings is about 2700 fathoms. .....- 
We were at length able,” he continues, “ to predict the nature of 
the bottom from the depth of the soundings with absolute certainty for 
the Atlantic and the Southern Sea.” And from these data he 
considers it an indubitable inference “that the red clay is essentially 
the insoluble residue, the ash, as it were, of the calcareous or- 
ganisms which form the Globigerina-ooze after the calcareous mat- 
ter has been by some means removed.” This inference he considers 
to have been confirmed by the analysis of several samples of 
Globigerina-ooze, “always with the result that,a small proportion of 
a red sediment remains, which possesses all the characters of the 
red clay.” Prof. Wyville Thomson further suggests that the removal 
of the calcareous matter may be due to the presence of an excess 
of carbonic acid in the bottom-waters, and to the derivation of this 
water in great part from cireumpolar freshwater ice, so that, being 
comparatively free from carbonate of lime, its solvent power for 
that substance is greater than that of the superjacent waters of the 
ocean. He might have added probability to his hypothesis if he 
had cited the observations of Mr. Sorby as to the increase of sol- 
vent power for carbonate of lime possessed by water under greatly 
augmented pressure*. 
Greatly struck with the ingenuity of this hypothesis, I turned to 
Prof. Wyville Thomson’s tabular statement of the facts in detail, 
and must own toa great feeling of surprise at the want of con- 
formity of these details with the assertions of universality and 
certainty of prediction which I have italicized in the above extracts. 
evidenced by the rounding into pebbles of what was elsewhere angular gravel. 
But it is even more conclusively shown by a comparison of the two serial 
soundings taken in the “cold area” (Nos. 52 and 64), which proves that the 
glacial stratum flows wp a slope in the former position (just as the cold under- 
stratum does in the Florida Channel), which it could not do unless it were in 
movement. That we did not trace the outflow of this cold stream into the 
great basin of the Atlantic, was simply, as I believe, because we were prevented 
from ascertaining the bottom-temperature on the line which I expected that 
flow to take after surmounting the ridge. 
* Proceedings of the Royal Society, vol. xii. p. 538. 
