REVIEW OF VOLCANIC ACTION. 357 
whole slopes with a flow of lavas, or, perhaps, many in succession. 
In this way the model cones of Kilauea vary their features and incli- 
nations. 
d. But besides these sources of change, another, equally common, is 
the opening of fissures around a vent. At the same time that cones 
are enlarging by overflowings, they are liable to ruptures of their 
sides in lines sometimes radiating with considerable regularity from 
the centre, and these fissures at once give exit to a flood of lavas, 
which spread around, forming a layer over the surface of the cone, 
and a dike of cooled rock in the fissure itself. These fissures, when 
starting, as they frequently do, from the central opening, must heighten 
the slopes ; for the dikes are like so many wedges driven into the sides, 
enlarging the surface and size, and consequently the angle of declivity. 
These various facts are matters of observation. When, therefore, 
cones are visibly accumulating by these processes, beginning at first 
around a point in an opened fissure, and attaining even rapid 
slopes in some instances; and when we observe that they continue 
enlarging by the same means, till even a mile in diameter, we must 
admit that lava cones may be a result of eruption. We must conclude 
that in the very earliest commencement of the ejections from a vent, 
there is a tendency to the formation of a cone, and that the same cone 
goes on increasing, and is a perpetually growing germ, becoming 
finally the future mountain. Kilauea gives us examples, on a com- 
paratively small scale, though still of no diminutive character, of the 
beginning and progress of the rising volcanic cone; and as the slopes 
of the larger mountain are very accurately represented in these be- 
ginnings, the same principle would seem to be sufficient for both 
cases. The study of the mountains themselves only confirms this 
view, presenting some new facts for our consideration. 
From Mount Loa we learn that, with the present slopes, its surface 
may be covered in any part by beds of lavas, and thus its size con- 
tinue increasing; and more than this, we learn from the eruption of 
which an account Is given on page 209, that its surface, with the exist- 
ing inclination, may be covered with a continuous bed of lava, twenty- 
five miles in length, extending from the summit to the interior plain 
of Hawaii. The average angle of the slope has been shown to be but 
six or seven degrees. But over declivities with this average angle, 
there are many places of much steeper descent, even to twenty-five 
degrees. Whatever that rapidity may be, the facts prove that the 
mountain is still enlarging by eruptions extending down its slopes. 
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