294 lioyal Society : — On the Nature of the 



Thus in the tWpest sounding in tlio \\hole Atlantic (that of 

 3875 fathoms, tukon on the voyage from St, Thomas to Bermuda), 

 as well as in the next two soundings of li'JtJO and 1^800 fathoms 

 respectively (the average of the three benig 3iill fathoms), the 

 bottom was " grey oozo ; " whilst in the next three soundings of 

 2SoO, :27<>(>, and 2G0U fathoms respectively (the average of the three 

 being U7ItJ fathoms, or nearly IdO fathoms less than the preceding) 

 the bottom was of " red day.*' Between JJermudaand the Azores, 

 again, there were six successive soundings between 27UU 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 28()0 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 2000 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-\\ ater and slowly settling down over particular areas, to 

 which it might be determined by the prevalent direction of the 

 bottom-llow, which would greatly depend in its turn npon the 

 ridge-and- valley conformation of the sea-bed. And the presence of 

 a small proportion of this material in the ordinary Glohiyerina-ooze, 

 whilst, where it is deposited in quantity, there are neither entire 

 Glohi(/en)i(ii 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 1 agree with Prof. AVyville 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 Glaucomtc — 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 1, drew atten- 

 tion to the fact that the grains of these green sands are for the most 

 part, if not entirely, internal casts of Poraminifera — 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. Jt was soon 

 afterwards shown by Prof. Bailey (TJ. .S.) that in certain localities 



* See my ' Shearwater ' Report in Proceed. Roy. Soc. 1872, vol. xx. p. .084. 

 t "Ueberden Griinsandund seino Erliiuterung, etc.," in Abbniidl. der konigl. 

 Akad. der Wissenscli. zu Ecrlin, 1855, p. 85. 



