249 
of Edinburgh, Session 1876-77. 
The Volcanic Debris in Ocean Deposits and some of the Products 
of its Disintegration and Decomposition. 
In a preliminary report to Professor Wyville Thomson, which 
has been published in the Proceedings of the Royal Society of 
London, I pointed out the wide-spread distribution of volcanic 
debris in ocean deposits and its probable influence in the formation 
of deep sea clays, and manganese nodules or depositions. In this 
paper I propose to treat of these subjects in more detail, and to 
give some of the results of observations which have been made 
since the above report was written. 
Pumice Stones. 
The form of volcanic debris most frequently met with in ocean 
deposits is pumice stone. 
Specimens of these stones, varying from the size of a pea to that 
of a foot-ball, have been taken in dredging at eighty of our 
stations. I have placed the position of these stations on a map, 
from which it will be seen that they occur all along our route. 
Near volcanic centres the dredge has frequently brought them 
up in great numbers, as off* the Azores in the Atlantic, oft* New 
Zealand and the Kermadec Islands, at several places among the 
Philippine Islands, off the coast of Japan, and elsewhere. As a rule, 
they are not numerous in shore deposits when these are distant 
from volcanic regions. In deposits far from land they are most 
abundant in deep-sea clays, from which the shells and skeletons of 
surface organisms have been all or nearly all removed. 
In the North Pacific the trawl brought up bushels of them from 
depths of 2300 and 2900 fathoms. Perhaps in no single instance 
have we trawled successfully on any of our deep-sea clays without 
getting numbers of these stones. If there be an exception it is in 
the North Atlantic. But here it is to be remembered that while 
we were investigating the conditions of the North Atlantic our 
attention had not yet been directed to the importance of detecting 
the presence of pumice, and we have not preserved such large 
samples of the North Atlantic deposits as of those of other regions. 
On the whole, pumice stones are more numerous in the Pacific 
than in the Atlantic deposits. 
In the Globigerina and other organic oozes, they are abundan 
