Rambles among the Channel Islands / by a Naturalist.

Date:
[1855?]
Catalogue details

Licence: Public Domain Mark

Credit: Rambles among the Channel Islands / by a Naturalist. Source: Wellcome Collection.

    139/402 (page 127)
    is geologists’ accounts are discrepant about it. So far as we have been able to examine its • structure, the following particulars may be j relied on. Its northern and southern boun- I daries are composed of rocks of syenite or [granite, and between these points a series of Uhe metamorphic rocks make their appearance, ■ constituting the main body of the island. Thus ; the primitive crystalline rock forms apparently I a hollowed interval, in which are contained a darge variety of rocks, derived from the altera- tion of the rocks, of the first series, or from intrusions into the former from below. At I each extremity the original granitic rock ap- ipears unaltered. The rocks contained between L these two points are remarkably diversified in Their character. They comprise every mixture l of micaceous schists with hornblende, actinolite, chlorite, talc, and potstone, and the frequent interchange of ingredients has caused, no doubt, I much of the perplexity of the different geo- dogical accounts given of this island. The : metamorphic influence also of the rocks which (have been intruded into these schistose and agil- ilaceous beds—that is, the alterations effected in their composition and structure by the forcible : injection of igneous rocks into their mass—tends i greatly to confuse the whole, and to produce .combinations of an intricate kind. The western