THE VOYAGE OF H.M.S. CHALLENGER 
•_>92 
or during relatively recent periods. The small dimensions and areolar structure of 
these fragmental volcanic materials admit of their being universally distributed over 
the Hoor of the ocean, and from the very fact that they are easily distributed by 
meteorological and oceanic agencies, they are especially characteristic of pelagic deposits. 
The second of these categories comprises all the rocks and minerals derived immediately 
from the disintegration of all continental and other lands by ordinary meteorological 
agencies, especially from the disintegration of crystalline, schisto-crystalline, and clastic 
rocks, which form the larger })art of the continental masses. These disintegrated 
materials are carried to the ocean by rivers and by winds, and are distributed to the 
deep sea by waves, tides, currents, and floating ice, but not so widely as the fragmental 
volcanic materials of the first category ; they are essentially characteristic of those 
deix)sits formed near continental shores and islands, which we have called Terrigenous 
Deposits.* 
(a.) Recent Volcanic Products. 
It is merely necessary to cast a glance at the synoptical Tables of Chapter II. to be 
convinced of the universal distribution of volcanic products in marine deposits. In 
runniug the eye down the column indicating the mineral particles, it will be seen that in 
nearly all the samples of the different types of deposits minerals and rocks occur which 
we recognise, from the study of terrestrial volcanoes, as having been derived from 
eruptions of the present or of relatively recent geological periods. It is not the same, 
however, with those rocks and minerals to which we attribute a continental origin, 
properly so called, for these last are especially abundant near land, and are almost 
wholly absent in the central parts of the great ocean basins. The fragmentary volcanic 
materials, while very often associated with the continental rocks and minerals near 
shore, are especially abundant in, and characteristic of, deposits far from land. It could 
not w'ell be otherwise, if the structure, conditions of formation, and mode of ejection of 
these volcanic materials be borne in mind. Whilst there may be a limit, towards the 
oj>en sea, to which the minerals and fragments derived from the disintegration of the 
continental masses can be transported, there is no such limit for the rocks and minerals 
l>rojected as dust, lapilli, and masses of pumice by terrestrial volcanoes, and though they 
may have a more restricted distribution, the same is the case with ejectamenta of sub- 
marine eruptions. 
In this connection it is but necessary to recall the distribution of active and recent 
volciinoes over the earth’s surface to show how favourably the ocean basins are situated 
for receiving the fragmentary materials ju’ojected into the air or the sea during eruptions. 
* Although we V»elieve that there are no esaential difTerences between the older and recent eruptive rocks, in the 
•enM formerly admitted by jtelrographers, there i« no doubt that each of these two groups, in the generality of the cases 
under consideration, offers some jieculiarities on which rests the subdivision adopted in this and other chapters. 
