Two Years And Three-
Quarters Afterwards, France, From Its Centre To The English
Channel, Would Have Been Again Desolated By An Earthquake
And An Island Permanently Upraised In The Mediterranean.
The space, from under which volcanic matter on the 20th
was actually erupted, is 720 miles in one line, and 400 miles
in another line at right angles to the first:
Hence, in all
probability, a subterranean lake of lava is here stretched out,
of nearly double the area of the Black Sea. From the intimate
and complicated manner in which the elevatory and eruptive
forces were shown to be connected during this train of
phenomena, we may confidently come to the conclusion, that the
forces which slowly and by little starts uplift continents, and
those which at successive periods pour forth volcanic matter
from open orifices, are identical. From many reasons, I
believe that the frequent quakings of the earth on this line
of coast are caused by the rending of the strata, necessarily
consequent on the tension of the land when upraised, and
their injection by fluidified rock. This rending and injection
would, if repeated often enough (and we know that earthquakes
repeatedly affect the same areas in the same manner),
form a chain of hills; - and the linear island of S. Mary,
which was upraised thrice the height of the neighbouring
country, seems to be undergoing this process. I believe that
the solid axis of a mountain, differs in its manner of formation
from a volcanic hill, only in the molten stone having
been repeatedly injected, instead of having been repeatedly
ejected. Moreover, I believe that it is impossible to explain
the structure of great mountain-chains, such as that of the
Cordillera, were the strata, capping the injected axis of
plutonic rock, have been thrown on their edges along several
parallel and neighbouring lines of elevation, except on this
view of the rock of the axis having been repeatedly injected,
after intervals sufficiently long to allow the upper parts or
wedges to cool and become solid; - for if the strata had been
thrown into their present highly inclined, vertical, and even
inverted positions, by a single blow, the very bowels of the
earth would have gushed out; and instead of beholding abrupt
mountain-axes of rock solidified under great pressure, deluges
of lava would have flowed out at innumerable points on every
line of elevation. [2]
[1] M. Arago in L'Institut, 1839, p. 337. See also Miers's
Chile, vol. i. p. 392; also Lyell's Principles of Geology,
chap. xv., book ii.
[2] For a full account of the volcanic phenomena which
accompanied the earthquake of the 20th, and for the conclusions
deducible from them, I must refer to Volume V. of the Geological
Transactions.
CHAPTER XV
PASSAGE OF THE CORDILLERA
Valparaiso - Portillo Pass - Sagacity of Mules - Mountain-
torrents - Mines, how discovered - Proofs of the gradual
Elevation of the Cordillera - Effect of Snow on Rocks -
Geological Structure of the two main Ranges, their distinct
Origin and Upheaval - Great Subsidence - Red Snow -
Winds - Pinnacles of Snow - Dry and clear Atmosphere -
Electricity - Pampas - Zoology of the opposite Side of
the Andes - Locusts - Great Bugs - Mendoza - Uspallata
Pass - Silicified Trees buried as they grew - Incas Bridge -
Badness of the Passes exaggerated - Cumbre - Casuchas -
Valparaiso.
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