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or otherwise according as the deposit is near or far removed from 
volcanoes. In these oozes they never occur so abundantly as in the 
clays. They are more or less masked and covered up by the accumu- 
lated remains of foraminifera, diatoms, or other surface organisms. 
In like manner they are obscured in shore deposits by river and coast 
detritus. Besides those specimens which are sufficiently large to 
be examined by the hand, we detected with the microscope minute 
particles of feldspar in all our ocean deposits. 
An inspection of the specimens which I have placed on the table 
appearance. Some of them have undergone much decomposition, 
while others are little altered. Some are coated with the peroxide 
of manganese, or have streaks of this substance running through 
them. They are the most frequent nucleus of the manganese 
nodules, to which I shall presently refer. Some specimens which 
were dredged from a depth of over three miles will, when dried, 
float for weeks in a basin of water; others, which have undergone 
partial decomposition, sink at once. 
They present a great variety of texture and composition. They 
are white, grey, green, or black in colour. They are highly vesi- 
cular, or rather compact and fibrous. There would appear to be every 
gradation from common feldspathic to dark green pyroxenic kinds. 
We find in them crystals of sanidin, augite, hornblende, olivine, 
quartz, lucite, magnetite, and titaniferous iron. Magnetic iron ore 
was found in all the specimens examined, either in crystals or in the 
form of dust. The other minerals vary in kind and abundance in 
the different specimens. The same crystals which we find in the 
pumice occur in all the kinds of ocean deposits. 
Sources of the Pumice Stones. 
The pumice stones which we find at the bottom of the sea have 
most likely all been formed in the air. Some of them may have 
fallen upon the sea; but the great majority seem to have fallen on 
land, and been subsequently washed and floated out to sea by rains 
and rivers. After floating about for a longer or shorter time they 
have become water-logged and have sunk to the bottom. Both in 
the North Atlantic and Pacific small pieces of pumice were several 
times taken on the surface of the ocean by means of the tow-net. 
