Fox and Somervail—Porphyritic Rocks of the Lizard. 75 
of micaceous schists. These indications continue for the next 
3800 yards, viz. to considerably south of Caerthillian, and on the 
foreshore are seen stones and boulders of typical porphyritic 
structure. 
Norru Carrtut~yran.—The most readily accessible place where a 
typical porphyritic rock may be seen in situ is immediately N.E. 
of the headland which bounds Caerthillian on the north. This spot 
can be reached with ordinary care from the top of the cliff, which 
is lower here than on either side. A quartzo-felspathic rock is 
exposed close under the soil, and a few yards below it are several 
bands alternating of porphyritic and granulitic rock much faulted. 
The darker bands are thickly studded with small well-defined crys- 
tals of felspar, which on the weathered surface project beyond the 
matrix. These bands can be traced for 20 yards in a N.W. and 
§.E. direction, much twisted. They extend in a §.W. direction to 
high-water mark and down the cleft to the south. 
SourH CaERTHILLIAN.—Some rocks apparently in situ on the fore- 
shore 70 to 100 yards south of Caerthillian Cove show crystals of 
felspar in their soft micaceous matrix. The adjoining cliffs show a 
porphyritic structure in a more compact rock. 
Pistrt Oco.—Rounding the Lizard Head, we can descend the cliff 
at this place, where we find a greenish porphyritic rock running 
N.W. and §.E., and 200 yards further east we reach the most 
southern point. 
Potrror.—When the shingle and seaweed have sufficiently left 
the coast, the porphyritic diabase discovered by Prof. Bonney can be 
traced running N.W. and §.H. for 150 to 200 yards. It is exposed in 
the micaceous and hornblendic schists in an intricate manner, appear- 
ing again and again at and near the base of the cliff and on the fore- 
shore both in Polpeor and the adjoining cove to the N.W. It can be 
traced in the mass of rock which at half-tide forms the eastern 
boundary of Polpeor beach, and through this on the foreshore still 
further east towards Polpeor Island. It appears again in Vellan 
Drang 200 yards 8.W. of Polpeor Cove in the strike of the Pistil 
Ogo Beds. 
Parn Vooss (locally Penvosz).—This cove directly north of the 
Balk Quarry is the place at which Prof. Bonney’s “ Granulitic 
Group” sets in, and continues with alternations of hornblende 
schist and serpentine to Kennack Beach. Here also the gabbros 
appear in mass, and here the porphyritic structure in the dark 
bands of this crystalline series may be seen to advantage. The 
foreshore is strewn with boulders recently fallen from the cliff, 
and the crystals of felspar in some of these are from one to two 
inches long and almost as broad. The same occurrence of crystals 
is seen in the cliffs, but not to such advantage as in the boulders. 
Potparrow.—Proceeding still eastward past Lean Water and 
Gothan Point or Whale Rock, we come to Polbarrow, and can trace 
porphyritic indications throughout this region. 
Kinrpown.—LHast of Cadgwith we also find crystals and felspar 
in the dark bands of the granulitic group. 
