J. Murray on Sea-bottom Deposits. 265 
regions, in others making up nearly a half of the deposit or 
formation. 
Pumice (the common feldspathic or the highly vesicular 
augitic variety) and scoria appear to be universally distributed 
over the bottom of the ocean, and to be abundant in most of 
the deep-sea clays and present in them all. In those clays 
farthest from continents and islands, sharks’ teeth, ear-bones of 
whales, other bones of whales, and bones of turtles (?) are very 
frequently found, all these having usually a more or less thick 
coating of peroxide of manganese. The following are the 
depths at which we have found these red and gray clays:— 
_ itis, however, not confined to these clays; it has been found 
in most of the other deposits and at all depths greater than 500 
clays it usually assumes the forms of minute grains, pellets and 
nodules. In those bottoms to which it gives a chocolate color, 
the higher powers of the microscope show : 
Town grains of manganese, often with a dark spot 1n the center. 
€ nodules vary from little pellets to masses of a large size 
and of several pounds in weight. In some regions everything 
at the bottom, even the bottom itself, would appear to be over- 
i by and impregnated with this substance. In the foregoing 
Ist, as at No. 318 and elsewhere, some of the nodules have 
