ncy of a DEEP ocean close to a rising continent bordered with
mountains, seems to indicate these opposite movements of rising and
sinking CLOSE TOGETHER; this would easily explain the S. Wales and
Eocene cases. I will only add that I should think there would be a
little more sediment produced during subsidence than during elevation,
from the resulting outline of coast, after long period of rise. There
are many points in my volume which I should like to have discussed with
you, but I will not plague you: I should like to hear whether you think
there is anything in my conjecture on Craters of Elevation (483/3. In
the "Geological Observations on Volcanic Islands," 1844, pages 93-6,
Darwin speaks of St. Helena, St. Jago and Mauritius as being bounded by
a ring of basaltic mountains which he regards as "Craters of Elevation."
While unable to accept the theory of Elie de Beaumont and attribute
their formation to a dome-shaped elevation and consequent arching of the
strata, he recognises a "very great difficulty in admitting that these
basaltic mountains are merely the basal fragments of great volcanoes,
of which the summits have been either blown off, or, more probably,
swallowed by subsidence." An explanation of the origin and structure of
these volcanic islands is suggested which would keep them in the class
of "Craters of Elevation," but which assumes a slow elevation, during
which the central hollow or platform having been formed "not by the
arching of the surface, but simply by that part having been upraised to
a less height."); I cannot possibly believe that Saint Jago or Mauritius
are the basal fragments of ordinary volcanoes; I would sooner even admit
E. de Beaumont's views than that--much as I would sooner in my own mind
in all cases follow you. Just look at page 232 in my "S. America" for a
trifling point, which, however, I remember to this day relieved my
mind of a considerable difficulty. (483/4. This probably refers to
a paragraph (page 232) "On the Eruptive Sources of the Porphyritic
Claystone and Greenstone Lavas." The opinion is put forward that "the
difficulty of tracing the streams of porphyries to their ancient and
doubtless numerous eruptive sources, may be partly explained by the very
general disturbance which the Cordillera in most parts has suffered";
but, Darwin adds, "a more specific cause may be that 'the original
points of eruption tend to become the points of injection'...On this
view of there being