507 
of Edinburgh, Session 1879 - 80 . 
The soundings of the “ Tuscorora ” and “ Challenger ” have 
made known numerous submarine elevations : mountains rising 
from the general level of the ocean’s bed, at a depth of 2500 or 
3000 fathoms, up to within a few hundred fathoms of the surface. 
Although now capped and flanked by deposits of Globigerina 
and Pteropod ooze, these mountains were most probably originally 
formed by volcanic eruptions. The deposits in deep water on either 
side of them were almost wholly made up of volcanic materials. 
Volcanic mountains situated in the ocean basins, and which 
during their formation had risen above the surface of the water, 
would assume a more or less sharp and pointed outline owing to 
the denuding action of the atmosphere and of the waves, and very 
extensive banks of the denuded materials would be formed around 
them. Some, like Graham’s Island, might be wholly swept away, 
and only a bank with a few fathoms of water over it be left on the 
spot. In this way numerous foundations may have been prepared 
for barrier reefs and even atolls. 
Those volcanoes which during their formation had not risen 
above the surface of the sea (and they were probably the most 
numerous) would assume a rounded and dome-like contour, * owing 
to the denser medium into which the eruptions had taken place, 
and the deposits which had been subsequently formed on their 
summits. 
In order to clearly understand how a submarine mountain, say 
half a mile beneath the sea, can be built up sufficiently near the 
surface to form a foundation on which reef-forming corals might 
live, it is necessary to consider attentively the 
Pelagic Fauna and Flora of Tropical Regions . — During the 
cruise of the “ Challenger,” much attention was paid to this subject. 
Every day while at sea tow-nets were dragged through the surface 
waters ; and while dredging they were sent down to various depths 
beneath the surface. Everywhere life was most abundant in the 
surface and sub-surface waters. Almost every haul gave many 
calcareous, siliceous, and other Algae ; great numbers of Eorami- 
nifera and Eadiolaria, Infusoria, Oceanic Hydrozoa, Medusae, 
Annelids ; vast numbers of microscopic and other Crustacea, Tuni- 
cates, Pelagic Gastropods, Pteropods, Heteropods, Cephalopods, 
* Scrope on Volcanoes, chap, viii, 
