294 ~~ Royal Society -—On the Nature of the 
Thus in the deepest sounding in the whole Atlantic (that of 
3875 fathoms, taken on the voyage from St. Thomas to Bermuda), 
as well as in the next two soundings of 2960 and 2800 fathoms 
respectively (the average of the three being 3211 fathoms), the 
bottom was “grey ooze ;” whilst in the next three soundings of 
2850, 2700, and 2600 fathoms respectively (the average of the three 
being 2716 fathoms, or nearly 400 fathoms less than the preceding) 
the bottom was of “red clay.” Between Bermuda and the Azores, 
again, there were six successive soundings between 2700 and 2875 
fathoms, in which the bottom was “grey ooze.” 
It is clear, then, that no constant relation exists between depth 
and the nature of the bottom. If not only eight ordinary sound- 
ings whose average was almost exactly 2800 fathoms, but the ex- 
traordinarily deep sounding of 3875 fathoms, gave a bottom of 
‘‘ grey ooze,” it surely cannot be “ an ascertained fact that wherever 
the depth increases from about 2200 to 2600 fathoms, the modern 
chalk formation of the Atlantic and other oceans passes into a 
clay.” 
Now, if this “ red clay” had the character of an ordinary river- 
silt, it would be quite conformable to my Mediterranean experience 
to regard it (as Prof. Wyville Thomson himself was at first disposed 
to do) in the light of a derivative from the land, diffused through 
the ocean-water and slowly settling down over particular areas, to 
which it might be determined by the prevalent direction of the 
bottom-flow, which would greatly depend in its turn upon the 
ridge-and-valley conformation of the sea-bed. And the presence of 
a small proportion of this material in the ordinary Globigerina-ooze, 
whilst, where it is deposited in quantity, there are neither entire 
Globigerine nor their disintegrated remains, would be perfectly con- 
sistent with the known destructive effect of the slow subsidence 
of a muddy sediment on many forms of animal life*, 
But I agree with Prof. Wyville Thomson in thinking that the 
remarkable uniformity of this deposit, coupled with its peculiar 
composition, indicates a different derivation ; and the suggestion I 
have to offer is based on its near relation in composition, notwith- 
standing its great difference in appearance, to Glauwconite—the 
mineral of which the green sands that occur in various geological 
formations are for the most part composed, and which is a silicate 
of peroxide of iron and alumina. 
It is well known that Prof. Ehrenberg, in 1853, drew atten- 
tion to the fact that the grains of these green sands are for the most 
part, if not entirely, internal casts of Foraminifera—the sarcodic 
bodies of the animals having been replaced by glauconite, and the 
calcareous shells subsequently got rid of, either by abrasion or by 
some solvent which does not attack their contents. It was soon 
afterwards shown by Prof. Bailey (U. 8.) that in certain localities 
* See my ‘Shearwater’ Report in Proceed. Roy. Soc. 1872, vol. xx. p. 584, 
+ “ Ueber den Griinsand und seine Erlauterung, etc.,” in Abhandl. der konigl. 
Akad. der Wissensch. zu Berlin, 1855, p. 85. 
