24 DYNAMICAL GEOLOGY. 
explosion took place (p. 206). During the eruption of 1866, some 
islets of lava rose above the sea in the middle of the bay, near the 
active vent. ‘The rock in these cases was compact, vitreous, and 
much cracked.* | 



















































































































































































































































































Fia. 61.—View oF THE PEAK OF TENERIFFE AND CoAst EROSION. 
Among submarine volcanic formations the tufts differ from those 
laid down on land chiefly in their organic contents; but partly also 
in their more distinct and originally less inclined bedding and in their 
tendency to the admixture of non-volcanic or ordinary mechanical 
sediment with the volcanic dust and stones. No appreciable differ- 
ence either in external aspect or in internal structure seems yet to 
have been established between subaerial and submarine lavas. 
Some undoubtedly submarine lavas are highly scoriaceous. There 
is no reason indeed why slaggy lava and loose, non-buoyant scorize 
should not accumulate under the pressure of a deep column of the 
ocean, At the Hawaii Islands, on 25th February 1877, masses of 
pumice, during a submarine volcanic explosion, were ejected to the 
surface, one of which struck the bottom of a boat with considerable 
violence and then floated. When we reflect, indeed, to what a con- 
siderable extent the bottom of the great ocean basins is dotted over 
with volcanic cones, rising often solitary from profound depths, we can 
believe that a large proportion of the actual eruptions in oceanic areas 
may take place under the sea. The immense abundance and wide 
diffusion of voleanic detritus over the bottom of the Pacific and 
Atlantic oceans, even at distances remote from land, as made known 
by the voyage of the “Challenger,” doubtless indicate the prevalence 
and persistence of submarine volcanic action, even though, at the 
same time, an extensive diffusion of volcanic débris from the islands 
is admitted to be effected by winds and ocean-currents. 
' Fouqué, Op. cit. 

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