REV. E. HILL ON THE ROCKS OF GUERNSEY. 413 
the only place known to me where it is worked. For building-pur- 
poses granite is actually imported from Jersey. This Cobo rock is, 
however, very handsome and, if sound, would make a very fine mate- 
rial for the architect. It is pink, coarsely crystalline, with felspar 
crystals ranging from ‘1 to ‘4 inch long, and consists of flesh-coloured 
felspar with much granular quartz and a sprinkling of black mica. 
Proof that this is truly igneous might seem needless, yet it has 
been described (Cambr. Phil. Soc. Proc. vol. iii. p. 78) as only an 
altered state of the red gneiss, so evidence must be given. <A bank- 
cutting on the Cobo Road some quarter of a mile from the coast 
shows grey gneiss and granite in almost immediate contact; and, 
in the latter a caught-up fragment of the former. The granite is, 
however, greatly decomposed and so split in places by platy jointing 
that it much resembles gneiss; only colour and composition marked. 
the fragment. Ifthen this evidence be unconvincing, let the doubter 
Fig. 2.—G ness caught up in Cobo Gramte. Shore south of Hommet 
Barracks. 
v—_ = + XN 
=) ( S50) — 5 
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+ 
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- -f- -l-- Hy \\\N) 
Grarnile 
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examine the shore south of Hommet barracks (fig. 2). Here among the 
rocks bared by a falling tide, the granite may be seen in actual con- 
tact with the gneiss that occupies the rest of Vazon Bay. The two 
is perfectly different; there is no difficulty in distinguishing them. 
The pink forms insulated masses in the grey, runs irregularly into 
it, flows round and includes portions of it, and presents all the 
. 
| 
, 
4 
4 
regular appearances of igneous intrusion. 
The relation of the Cobo granite to the rocks onits east and north 
is less easy to settle. In a quarry at the west end of Les Genats 
Road there appears to be a contact between the blue dioritic rock 
which is quarried, and granite. If so, the granite should be the 
later, as it seems to show a considerable alteration in character along 
the contact, while the blue rock remains unchanged. At the northern 
limit in Portinfer Bay it is intersected by a couple of bands of a 
dioritic rock (different from the common blue variety), but I see no 
evidence to show which isthe later. Ina quarry east of Vale church 
is a dyke of pink granite that resembles the Cobo rock. On the 
whole I have little doubt that the Cobo granite is later than the 
diorites. 
Q.J.G.8. No. 159. QF 
ee Se eee 
