266 J. Murray on Sea-bottom Deposits. 
been described with a little detail: The varieties which are 
most commonly procured may be here mentioned: 
(a.) Nodules of a black-brown color throughout, the manga- 
nese being laid down in concentric layers, which are evident 
from their enclosing lines of red clay. 
(6.) Nodules having a nucleus of pumice which is surrounded 
by concentric layers. the original nucleus being often very 
deeply impregnated by spider-like ramifications of the manga- 
nese, or nearly the whole pumice may be replaced by manga- _ 
e 
nese. hen pieces of bone have formed the nucleus we have 
much the same state of things. The compact bone of the tym- 
panics of cetaceans does not, however, appear to alter so rapidly 
as other bone; and hence it may be that we get ear-bones in 
such great numbers. 
Sharks’ teeth of all sizes (one was four inches across the base) 
are frequent, and are sometimes surrounded by concentric layers 
of nearly an inch in thickness. A siliceous sponge (Farrea) 
was found imbedded in two inches. 
p 
nese. This was in a depth of from 1100 to 1575 fathoms. of 
In 670 fathoms, off the Desertas, the dead shells, pieces 
_ tin some of the Radiolarian oozes, and in other pee bi 
have found the manganese more abundant in the upper ay 
than in the lower, and vice versd. he man- 
The following are the localities where we have met the 
ganese in greatest quantities: 
Off the “Oncars aaande: Mid-Atlantic, between Canary are 
Virgin Islands; southwest of Australia; north and sout South 
Sandwich Islands; north of Tahiti; generally in the 
acific in our course between Tahiti and Valparaiso. 
