12
GEOLOGICAL REMARKS.
[Chap. I.
1841
chimney-like cavity, in the steep face of the igneous rock; the lower portion having been removed has left its cast in the rock, a foot in diameter, to the extent of seven feet. In the soil beneath I found a fragment of it, having an opaline appearance.
The top of this cliff is about forty feet above the river, which is here somewhat narrower, and the ravine not more than sixty yards wide. About two miles from Rose Garland I saw excavations in a low bank of scoriæ, near a curve in the Derwent, where there is a long low island in the centre of the river, lying parallel with its banks, from which two silicified trees had been removed some years ago: they had all been vertically imbedded.
It seems, therefore, quite evident that they were actually growing when the lava in which they are imbedded overflowed the plain. It is a curious fact connected with this subject that, although large external roots are found on some of those fossilized trees, no branches have ever been discovered; as if it required a certain thickness of trunk to resist the effects of the incandescent matter; and the circumstance of finding these trees in an erect position, would seem to prove that the fossilization occurred at the same time with, and was therefore in some manner produced by, the overwhelming matter; and it would be an interesting fact to ascertain whether the roots of any of these trees are still adherent to them, or whether any movement of the whole mass down the valley, during the process of solidification, has removed
