= 
stratum of their remains. No doubt each haul of the dredge which — 
brought up so many bones represented the droppings of many genera- 
tions. The successive stages of manganese incrustation point to along, 
slow, undisturbed period, when so little sediment accumulated that the 
bones dropped at the beginning remained at the end still uncovered, 
or only so shghtly covered as to be easily scraped up by the dredge. 
In these deposits, moreover, Mr. Murray has found numerous minute 
spherular particles of metallic iron which he regards as of cosmic 
origin—portions of the dust of meteorites which in the course of 
ages have fallen upon the sea-bottom. Such particles no doubt 
fall all over the ocean; but it is only on those parts of the bottom 
which, by reason of their distance from any land, receive accessions 
of deposit with extreme slowness—and where therefore the present 
surface may contain the dust of a long succession of years—that 
it may be expected to be possible to detect them. 
The abundant deposit of peroxide of manganese over the floor of 
the deep sea is one of the most singular features of recent discovery. 
It oceurs as an earthy incrustation round bits of pumice, bones, and 
other objects (Fig. 167). The nodules possess a concentric arrange- 

Fic, 167.—Mancanrsz Nopurrs. Fioor or tHe Norra Paciric. Two-rurrps 
NATURAL SIZE! 
A, Nodule from 2900 fathoms showing external form. B, Section of nodule from 2740 
fathoms showing internal concentric deposit round a fragment of pumice, 
ment of lines not unlike those of urinary calculi. That they are 
formed on the spot, and not drifted from a distance, was made abun- 
dantly clear from their containing abysmal organisms, and enclosing 
more or less of the surrounding bottom, whatever its nature might 
happen to be. Quite recently Mr. J. Y. Buchanan has dredged similar 
small manganese concretions from some of the deeper parts of Loch 
' From the Reports of the “Challenger” Expedition, The detailed investigation by 
Messrs, Murray and Renard of the deep-sea deposits obtained by this expedition will 
form oue of the most important contributions yet made to our knowledge of the chemistry 
of the oceanic abysses, 
‘a 
Ce 
< 
ape DYNAMICAL GEOLOGY. —— [Boox III. _ 


