76 ~=Fox and Somervail—Porphyritic Rocks of the Lizard. 
Carrieon.—Here Prof. Bonney’s porphyritic dyke’ is seen about 
100 yards south of the Poltesco Serpentine Factory. 
Passing Caerleon Cove, we climb up the hill by the Coast-guard 
path, cross the rocky slope above “ Little Cove,” and scramble down 
into the next small cove north of a projecting serpentine headland 
called in the Parish Map Polbream Point. Here we find rocks with 
large crysials of felspar, both in situ and in boulders scattered over 
the rocky foreshore for the next 300 yards northward. 
Cavouca.—The Parish Map gives the name of Cavouga to the 
serpentine rocks running out to sea 100 yards north of Polbream 
Point, and as the rocks containing large crystals of felspar occur on 
each side of these serpentine rocks, it may be an appropriate name 
by which to designate this region. 
There are two exposures of these large-crystalled porphyries in 
situ at the foot of the cliffs; the first about 90 yards S.W. of 
Cavouga Rocks, the second about 200 yards north of them, or say 
600 yards N.E. of Poltesco Serpentine Factory. The first of these 
appears to cut the serpentine, and can be traced up the cliff, the 
darker bands containing both large and small crystals of felspar at 
various angles, and the associated lighter bands resembling the 
quartzo-felspathic bands of the ‘‘Granulitic Group.” The second 
exposure north of Cavouga Rocks resembles three dykes cutting 
through the serpentine; but, as Colonel MacMahon suggests, it 
may be one dyke which by pressure has been doubled up on itself. 
Between and on either side of these two exposures the darker bands 
of this crystalline series of rocks show from time to time distinct 
crystals of felspar in the massive rocks as well as in those which 
appear to cut the serpentine as dykes. On the foreshore are many 
boulders so studded with crystals as to resemble mosaic, the crystals 
occasionally reaching a length of nearly six inches and a breadth 
of from two to three inches. One boulder had some of the crystals 
beautifully tinted with red. 
Kennacx.—In proceeding east to Kennack, we trace the crystals in 
the dark bands of the granulitic group, and on reaching the beach we 
find the porphyritic structure very marked in some isolated masses of 
the same group, one of which Prof. Sedgwick described as a “ Green- 
stone porphyry.” * North of these in a low cliff we trace a similar 
structure. 
GREEN SappLE.—About 500 yards E.S.E. of the thatched shed at 
the extreme east of Kennack Beach there is another exposure of 
rock with large crystals of felspar resembling a dyke cutting the 
serpentine. The foreshore is here also strewn with boulders of 
porphyritic rock. 
Summary. 
The crystals of felspar are found to be most numerous in those 
rocks which lie in the closest proximity to the gabbro and serpentine ; 
1 Quart. Journ. Geol. Soc. Nov. 1877, p. 900. 
* Trans. Cambridge Phil. Soc. vol. i. p. 18. 
