The Ordovician and Silurian Rocks of the Kilbride Peninsula (Mayo)

Abstract

I. Introduction. The Kilbride area with which this paper deals lies some 5 miles to the south of the Glensaul area described by us in 1910. Its limits are very sharply defined. It forms a peninsula bounded by two long inlets from the south-western corner of Lough Mask, the northern one being known as Derry Bay or Derrypark Bay, the southern as Kilbride Bay. It has a length from east to west of about 4½ miles, and a breadth of about a mile and a half. It ends to the west in the alluvial tract through which the Finny River runs. From this low ground the land rises rapidly to a ridge which attains its highest point at Knock Kilbride (1230 feet). Farther east is another eminence (Knocknamuck), and then the ground sinks slowly through Fox Hill to the shore of Lough Mask. The descent from the high ground to Derry Bay on the north is far steeper than that to Kilbride Bay on the south, a fact intimately associated with the geological structure of the country. Little has been written about the geology of this area. Some description of it is given in the Memoirs of the Geological Survey. The igneous rocks are referred to as being everywhere felsite; the presence of ash is mentioned; and allusion is made to the finding of Llandovery fossils at several points on the southern side of the peninsula. In the ‘Annual Report of the Geological Survey for 1896’ (pp. 49–51) a general