There appears much
probability in the view first proposed by Mr. P. Scrope, that when
the barometer is low, and when rain might naturally be expected to
fall, the diminished pressure of the atmosphere over a wide extent
of country might well determine the precise day on which the earth,
already stretched to the utmost by the subterranean forces, should
yield, crack, and consequently tremble. It is, however, doubtful
how far this idea will explain the circumstance of torrents of rain
falling in the dry season during several days, after an earthquake
unaccompanied by an eruption; such cases seem to bespeak some more
intimate connexion between the atmospheric and subterranean
regions.
Finding little of interest in this part of the ravine, we retraced
our steps to the house of Don Benito, where I stayed two days
collecting fossil shells and wood. Great prostrate silicified
trunks of trees, embedded in a conglomerate, were extraordinarily
numerous. I measured one which was fifteen feet in circumference:
how surprising it is that every atom of the woody matter in this
great cylinder should have been removed and replaced by silex so
perfectly that each vessel and pore is preserved! These trees
flourished at about the period of our lower chalk; they all
belonged to the fir-tribe.
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