On some dykes in east Aberdeenshire

Abstract

Within the bounds of the ‶Peterhead″ Granite, a mass some 53 square miles in extent, a number of dykes are exposed. With three exceptions, these occur on the coastal section, but, as the geological formations inland are greatly obscured by drift and alluvium, attempts to establish proof of the persistence or otherwise of the dykes have failed, unless in the case of one rock type which appears to stretch as a dyke from Buchan Ness, beyond the limits of the granite, to the village of Rhynie. Previous work on these intrusions is confined to notes on exposures of dolerite and quartz porphyry in the Memoir of the Geological Survey accompanying sheet 87 (1),1 records of dolerite in the Memoir of 76 (2), and descriptions, together with an analysis, of quartz-dolerite given in Memoirs 86 and 96 (3), the presence of most of the dykes not being mentioned. Twenty-five occurrences of dykes within the granite were examined. Two of these were quartz dolerites, nine felsites and quartz porphyries, and fourteen porphyrites. They all show chilled margins against the granite, the latter being apparently unaffected by the intrusions. Eight quartz-dolerite dykes outside the limits of the granite were also examined. The Quartz Dolerites. After examination of the two exposures of this rock within the granite other eight dolerite dykes, mapped by the Geological Survey between Rhynie and Buchan Ness, were investigated in the field and further dealt with as a series in the laboratory. Dr H. H. Read suggests, in the Huntly