The geology of the Colwyn Bay district: a study of submarine slumping during the Salopian period

Abstract

The area described in this communication is bounded on the north in part by the coast of Colwyn Bay and farther west by the base of the unconformable Carboniferous rocks. It extends southwards for nearly five miles and westwards to the estuary of the River Conway near Llansantffraid Glan-Gonway. It is included in the area recently described by Professor Boswell (1935). The town of Colwyn Bay stands at the foot of a steep crescentic scarp which marks an old cliff-line, the base of which is concealed by boulder-clay. The upper edge of the scarp is nearly 500 feet above sea-level, and southward of it extends an undulating plateau culminating on Mynydd Du, 4½ miles to the south, in low twin summits at 1133 and 1139 feet above sea-level. The plateau is traversed by steep-sided valleys eroded by streams which flow northwards towards the bay or westward into the estuary of the River Conway. The watershed between the Conway and the bay drainage pursues a zigzag course in a general north-west and south-east direction across the centre of the area. It runs for long distances through the high ground occupied by the slumped beds described below. The plateau is mainly upland pasture diversified by rocky knolls and ridges usually covered by gorse and bracken. In some cases the trends of the ridges indicate broadly the general structure of the area, which in others is revealed by long scarps of bare rock, alternating with narrow strips of cultivated ground or pasture. The