Wyville Thomson—General Ocean Circulation. 353 
bone, or an otolith, or a piece of siliceous sponge, or more fre- 
quently a fragment of pumice. These nodules are evidently 
formed in the clay, and the formation of the larger ones and 
the segregation of their material must have taken a very long 
time. Many of the sharks’ teeth to which I have alluded as 
forming the nuclei of the nodules, and which are frequently 
brought up uncoated with foreign matter, belong to species 
which we have every reason to believe to be extinct, Some 
teeth of a species of Carcharodon are of enormous size, four 
inches across the base, and are scarcely distinguishable from 
the huge teeth from the Tertiary beds of Malta. It is evident 
that these semi-fossil teeth, from their being caught up. in 
numbers by the loaded line of the trawl, are covered by only 
a very thin layer of clay. 
Another element in the red clay has caused great speculation 
and interest. Ifa magnet be drawn through a quantity of the 
fine clay well diffused in water, it will be found to have caught 
on its surface some very minute magnetic spherules, some appa- 
rently of metallic iron in a passive state, and some of metallic 
nickel. From the appearance of these particles, and from the 
circumstance that such magnetic dust has been already detected 
in the sediment of snow-water, my colleague Mr. Murray has 
a very strong opinion that they are of cosmic origin—exces- 
sively minute meteorites. They certainly resemble very closely 
the fine granules which frequently roughen the surface of 
the characteristic skin of meteorites, and from their composi- 
tion and the circumstances under which they are found there is 
much to be said in favor of this view. I cannot, however, 
hold it entirely proved; there can be little doubt, from the 
universal presence of water-logged and partially decomposed 
pumice on the bottom, and from the constant occurrence of par- 
ticles of volcanic minerals in the clay, that the red clay is 
formed in a great measure by the decomposition of the lighter 
products of submarine volcanoes drifted about by currents, and 
finally becoming saturated with water and sinking; and it is 
well known that both iron and nickel in a metallic state are fre- 
quently present in minute quantities in igneous rocks. I think 
It is conceivable that the metallic spherules may be derived 
m this source. : 
0 far as we can judge, after a most careful comparative ex- 
amination, the deposit which is at present being formed at 
extreme depths in the ocean does not correspond, either in 
Structure or in chemical composition, with any known geologi- 
cal formation; and, moreover, we are inclined to believe, from 
 @ consideration of their structure and of their imbedded organic 
remains, that none of the older formations were laid down at 
nearly so great depths—that, in fact, none of these have any- 
