The Avonian Succession in the South of the Isle of Man

Abstract

The Carboniferous rocks described in this paper occur within an area some 8 to 9 square miles in extent surrounding the ancient town of Castletown. The district is coastal and low-lying, a considerable portion being less than 100 feet above sea-level. The highest ground lies north-west of Ballasalla, where a few small tracts rise slightly above 200 feet. The solid rocks are for the greater part obscured by a thick covering of drift, alluvium, or blown sand, and the chief outcrops are on the coast, usually between tide-marks. Most of the inland outcrops are confined to quarries lying west of the village of Ballasalla, to the Silver Burn, and to its tributary the Awin Ruy. The heavy growth of seaweed and the honeycombing of the boring molluscs near low-water-mark render difficult the collecting of fossils, which, in many places, are also partly or totally destroyed by dolomitization, especially near the more important faults. Stretches of sand, shingle, and displaced joint-blocks break the continuity of the beds in the cliffs and on the foreshore, so that direct measurement of thickness is often impossible. The Carboniferous rocks are bounded on the north-west by the Port St. Mary—Arbory Fault, which extends from Perwick Bay to near Ballashimmin (a distance of 5 miles), and with variable throw brings up the Manx Slate Series. Elsewhere on land the boundary is an unconformable or faulted junction with the Lower Palæozoic rocks. A similar junction probably exists a short distance below low-water-mark between the mouth of the