VOLCANIC GROUP OF ST. DAVID’S. 301 
be for a moment doubted. The clear exhibition of a double fault 
is also instructive as affording the key to the obscurer sections at 
Porthclais. 
Of these, the one on the east of the stream shows no intrusion; 
the granite is massive, the slates are massive; but the foot or so 
between them is rotten and waterlogged ; the granite is undoubtedly 
over the slates in the slanting junction. On the opposite side of the 
stream the granite is in like manner over the conglomerate, but 
does not intrude into, or alter it. Both junctions are due to one 
overthrust fault along the continuation of the line which was traced 
‘at Nun’s Chapel. Im any case the conglomerate is out of place 
here, and there must be' another, no doubt connected, fault to bring 
it there, as at Ogof Llesugn. In the next small section to the north, 
where the granite and slate approach, there is 3 feet between the 
solid rocks, occupied in part by decomposed slate and in part by 
decomposed granite; here the latter underlies, and the fault is not 
reversed. On the other side of the granite tongue, where it touches 
the conglomerate again on the north, there is a complication of 
faults; next to the solid granite comes a mass partly decomposed, 
next a mass of the quartz-felsite, and then, on the other side of about 
6 inches of broken material, the unaltered solid conglomerate. 
There is another junction on the opposite side of this conglomerate, 
where the granite comes on again; butits natureis notseen. Thus 
the boundaries of the series of rocks in question have been examined 
at all the chief points in the whole circumference, and there is not 
a single spot where intrusion is suggested, much less shown, or 
where the volcanic ashes are bound in any way to the Cambrian 
conglomerate. 
But is there nothing in the idea of an isocline on the western 
side which should show that the conglomerate always follows the 
silvery schists or their equivalent? I have rowed round the whole 
of the coast from Porthlisky to the Penmaen-Melyn, and have 
examined a large portion of it on land, and have been enchanted 
with the glorious confusion of the volcanic masses there exhibited. 
Here are the evenly bedded massive agglomerates, here great 
hummoceks of dark lava protruding into the sea, here columnar and 
spheroidal dykes, now unstratified agglomerates with beds thrown 
off on either side, and now nearly horizontal well-bedded purple 
ashes, overlain by a lava-like rock, but all without a sign of a 
regular feld, which, amongst such rocks, would be almost impossible 
to conceive. Nor is the similarity of the two rocks on the supposed 
opposite sides of the fold so great ; on the west they are uniformly 
silky and pink, on the east, next the granite, they are of all kinds, 
including many very soft and variously coloured ; but these bear 
only the faintest resemblance to anything on the eastern side of the 
granite at Caerbwdy, where only the topmost red ashes are at all 
like them, while the lower ones which tend to become porcellanites, 
are quite peculiar in the St. David’s district. 
Such are the proofs that the whole series below the Cambrian 
ee nar oa eee 
