Crosby. ] 162 [March 5, 
found during the whole cruise only one or two sharks’ teeth and per- 
haps one tympanic bone. In shore deposits they were even more 
rare. These facts taken with others that will at once suggest them- 
selves, go to show, as might be expected, that the shore deposits ac- 
cumulate faster than the organic oozes, and these last faster than the 
deep sea clay.” : 
Concerning the origin of the clay deposit very diverse opinions 
have been held. Prof. Wyville Thomson justly considers that the 
uniform character of the deposit renders untenable the view that it 
is ‘‘ the most minutely divided material, the ultimate sediment, pro- 
duced by the disintegration of the land, by rivers and by the action 
of the sea on exposed coasts, and held in suspension and distributed 
by ocean currents.”” The water at those great depths has been found 
to contain rather more than the normal amount of carbon dioxide, 
although animal life is much less abundant on those parts of the sea- 
floor than over the ooze areas, diminishing rapidly beyond a depth 
of 2000 fathoms; and Prof. Wyville Thomson suggests that a large ~ 
part of this water has been last at the surface, in the form of cireum- 
polar fresh-water ice, and hence, though fully charged with carbon 
dioxide, it may be comparatively free from calcium carbonate, and 
therefore capable of dissolving considerable amounts of that salt, 
There is no dearth of Foraminifera, or of shell-bearing pelagic Mol- 
lusca (Pteropods), in the water over the red clay areas; but when 
the animals are dead their shells are entirely dissolved during the 
slow descent to the bottom, or soon after. It has been ascertained 
that when dissolved in weak acid these shells from the bottom leave 
a residue of about one per cent., possessing all the essential char- 
acters of the red clay. Putting these facts together, Prof. Wyville 
Thomson, in 1874, reached thé conclusion that the red clay is es- 
sentially the insoluble residue, the ash, as it were, of calcareous 
organisms such as form the globigerina-ooze. 
Dr. Wm. B. Carpenter, on the contrary, while admitting the de- 
composition of the organic remains by carbon dioxide, asserts the 
a priori improbability of their affording a true ash or residue of the 
quality and in the quantity required; and is hence led to question 
the adequacy of this explanation of the origin of the red clay. He 
considers the clay as a hydrous silicate of aluminum and iron 
analogous to glauconite, the chief constituent of greensand, the differ- 
ence in color appearing “to depend upon the degree of oxidation of 
the iron”; shows that a precisely similar ochreous material sometimes 
forms interior casts of foraminifera shells; and concludes that the 
