On a Small Section of Felsitic Lavas and Tuffs near Conway (Caernarvonshire)

Abstract

T he felsites of Conway Mountain were described by Prof. Bonney more than 16 years ago. Among specimens which I collected in North Wales in 1877, but from which sections have only recently been prepared, there are a few which may be of interest, since they were procured at short intervals from a point at the mouth of the River Conway, and may be regarded as representing the southern portion of the felsite near the fault which, on the Geological Survey map, is shown to separate the felsites of Conway Mountain from those of Diganwy, throwing the latter a considerable distance to the north. The spot at which the specimens were collected is marked Bodlondeb on the Ordnance Survey map. A path runs round this point, bounded on the west by an exposure of rock which has been dressed back so as to form a low natural wall, while a lower wall has been built between the eastern side of the path and the estuary (see map, p. 172). The specimens, or small chips, were consecutively numbered in the order in which they were collected, from south to north. On the south the felsite is succeeded by Bala Beds, which about a mile to the west are marked on the Geological Survey map as dipping 60° southward, but at Bodlondeb the felsites appeared to dip at a higher angle. No. 1 is a pale pinkish-grey rock, somewhat resembling the yellowish felsite which occurs to the west below Castell Caer Seion. The