74 Fox and Somervail—Porphyritic Rocks of the Lizard. 
V.—On THE OccuRRENCE oF PorpHyritic STRUCTURE IN SOME 
Rocks or tHe Lizarp Dtisrrict.! 
By Howarp Fox, of Falmouth, and Avex. Somervatt, of Torquay. 
EING the fortunate possessors of Prof. Bonney’s valuable papers ? 
on the Lizard Serpentines and Schists in a pamphlet form, 
we examined the coast this spring somewhat minutely from Polurrian 
Cove on the west to the Blackhead on the east of the Lizard Point. 
We had tracings of the entire coast in our pockets, taken from the 
25 inch Parish Maps, and owing to fine weather, and a favourable 
state of the coast, we were able to visit some of the less accessible 
rocks, and to trace some beds which at times are covered with sea- 
weed and shingle or débris from the falling cliffs. Prof. Bonney’s 
porphyritic diabase had been previously identified by one of us after 
along search over the 18 acres of rocks and boulders exposed at 
Polpeor at low-water spring-tides. We made ourselves familiar 
with this rock, and were thereby enabled not only to trace it further, 
but to recognize a porphyritic structure in many dykes and intrusions 
along the coast, and also in the darker bands of Prof. Bonney’s 
“ Granulitic Group.” 
Commencing at Polurrian, the most westerly point, we will proceed 
eastward, noting the chief localities where the porphyritic structure 
may most readily be observed. 
Ve tian Heap. —About 250 yards N.W. of the granitic vein marked 
on the Ordnance Map, near the base of the cliff and opposite an 
island, some narrow porphyritic dykes occur in the midst of bands of 
disintegrated serpentine, steatite, etc., and quartzose rock. 
Goop GastoL (?).—At the inner end of a little cove about 800 
yards §.E. of Oliver’s Refreshment Room at Kynance Cove there 
are some dykes with a few crystals of felspar scattered through 
their compact dark matrix. 
Hoxzestrow.—On the foreshore at the southern end of this land 
slip and a little N.W. of Pentreath Beach are several masses of 
banded crystalline rocks in situ resembling the ‘ Granulitic Group.” 
In these rocks may be discovered by careful search felspar crystals 
scattered through the matrix of the darker bands. 
PrenrreatH Bracn.—At the extreme north end of this beach a 
granitic vein runs up the cliff. Adjoining are some trap dykes also 
cutting the serpentine. About 100 yards south of this point a por- 
phyritic dyke may be seen at low-water running in a N.W. and 
S.E. direction. This dyke is again found in a chine in the 
cliff in a line with its strike. At the south end of this 
beach occurs the junction of the serpentine with hornblende 
schist. About 100 yards south of this junction we find indications 
of porphyritic structure in the massive cliffs, here chiefly composed 
1 An Abstract of this paper was read before the British Association, Section C. 
(Geology), Manchester, September 1887. 
* Quart. Journ. Geol. Soc. Noy. 1877, pp. 884-928, and Feb. 1888, pp. 1-24. 
