(Scale 6 inches=1 mile.) 
Fig. 3.—Section (partly deat) from Penera Head to Porthalla. 
462 J. H. COLLINS ON THE SERPENTINE AND 
The general strike of the Lizard rocks referred to 
is a few degrees to the north of west, the preyail- _ 
ing dips being to the east of north. At Porthalla, 
on the contrary, the general strike is to the east 
of north, 2. ¢. as nearly as possible at right angles 
to the direction of the Lizard rocks. 
The band of granulite in the ‘“‘micaceous group,” 
which appears to Prof. Bonney to be a conform- 
able bed of that series formed under similar con- 
ditions to the granulitic group of the Lizard, 
ji seems to me to be distinctly unconformable, and 
Granule saa to have the character of an intrusive vein pene- 
ETE. trating the “talcose” schists, as indicated in 
sections figs. 2 and 3. I believe, in short, that the ~ 
Lizard rocks may be Archean, but that those of 
Porthalla are of mnch later origin and most pro- 
bably Lower Silurian. 
The rocks beyond Hickes’s quarry offer no 
special feature of interest. As already stated, 
they consist mainly of hornblende schist of the 
banded type interspersed with occasional bands 
of serpentine, the largest exposures of which 
latter are in the broken ground which succeeds 
the fault at Porthalla and in the little cove to the 
south of Polkerris. In the section fig. 3 I give an 
ideal representation of the country from Porth- 
alla to Pencra Head, on a line which passes a 
little to the south of this cove. This section is 
given as the result of a careful examination of the 
country on several different occasions. It is, of 
course, partly hypothetical ; but I believe it is in 
the main correct. 
N.W. 
Porthalla. 
Porthalla slates. 
Poikerris 
Veins of Gabbro. 
These I have not yet seen in a perfectly satis- 
factory manner; but there are several bands of 
what I believe to be gabbro traversing the schist 
between the quarry and Dranna Point. I have 
examined the cliffs on several occasions, with the 
view of ascertaining the true nature of these 
veins; but the swell has always prevented me 
from taking the boat close up to the rocks. I 
Pencra, oan Ui have, however, repeatedly found on the shore, 
aa close to the quarry, loose masses of the schist, tra- 
versed by veins of undoubted gabbro. In appear- 
ance the gabbro does not seem to differ at all 
from the “ Newer gabbro” of Coverack described 
by Prof. Bonney. 
Hornblende slates and schists with interbedded serpentines &c., supposed Lower Silurian. 
8.B. 
