Abstract

The area described in the following paper is, in the main, a prominent ridge some 4 miles long, forming the extreme north-western portion of Somerset and stretching from Portishead in the northeast to Clevedon in the south-west (Pl. XXXIX, fig. 1). It is separated from the Clifton—Clevedon ridge by the Gordano valley; but, as one proceeds south-westwards, the two ridges are seen to approach and eventually come together at Clevedon.

The main part of the ridge is geologically very simple, consisting of Old Red Sandstone overlain by the Carboniferous Limestone Series dipping south-eastwards; but at each end the structure becomes very complicated and difficult of interpretation. Owing to this fact, it has been thought desirable to describe the main part of the ridge first.

The district was mapped by Sanders on the scale of 4 inches to the mile, and the Geological Survey for the 1-inch map made but slight alteration in his lines. Little has been written, except about the Portishead end of the ridge. This, however, was described in considerable detail by Prof. C. Lloyd Morgan, and, as his paper deals fully with the earlier work, it will not be necessary to repeat the references to this subject. Arthur Yaughan's work on the palæontological sequence in the Carboniferous Limestone of the Bristol area led him to determine the horizon of the rocks at the chief exposures throughout the district, but he did not attempt any general explanation of the geological structure. Some account of the chief exposures will