File:The Quarterly journal of the Geological Society of London (12737057674).jpg

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T. G. BONNET ONT THE SERPENTINE AND
had altogether twenty-one slides prepared from different localities* ;
and Mr. S. Allport has kindly permitted me to use others from his
collection, admirably cut by himself. I have also procured, for
comparison, several others from foreign serpentines. A suspicion
of the true nature crossed my mind in 1874, when examining a slide
from the black serpentine near Cadgwith (no. 10). A specimen col-
lected in 1875 at Coverack Cove rendered the conjecture a certainty ;
and a further confirmation was given by my visit to the Ariege, and
by specimens collected at other Cornish localities, in 1876. In the
following description I shall not take the slides in the order in
which their localities are mentioned above, but group them so as
best to tell their story.
Coverack Cove (no. 12). — This serpentine is often considerably
decomposed ; but my slide was cut from a well-preserved specimen .
To the eye it is a dull mottled red-and-green rock, with ill- defined
flakes in the latter part of a silky bronzitic mineral. With the
microscope, we see that about two-thirds of the rock consists of a
clear transparent mineral of a texture rather like frosted glass, tra-
versed by reticulated veins of a golden- coloured (varying to greenish
and reddish-brown) serpentine. These serpentine veins run together
sometimes like matted roots, and apparently coalesce like the pseu-
dopodia of foraminifera (fig. 8). As described in the gabbro above,
Fig. 8. — Portion of a Slide of
Serpentine from Coverack
Cove.
Fig. 9. — Portion of a Slide of
Lherzolite .Etang de Lherz,
Ariege), showing the form-
ation of Serpentine.
The granulated part unchanged olivine ; the rest rather fibrous serpentine.
(Magnified 50 diameters, about.)
there is the same deposit of iron peroxide (here reddish) parallel to the
sides of the fibres, which in the larger patches of serpentine seem
either to disappear or to be aggegated in dusky patches. On applying

• These, with the others used in this paper, have been excellently prepared