VII.— The Heads of Ayr Vent

Abstract

I. INTRODUCTION The twin headlands of the Heads of Ayr are located on the coast four miles south of the town of Ayr. They occupy about half-a-mile of coast and provide excellent vertical (cliff) and horizontal (wave-cut platform) sections through a volcanic vent of Carboniferous age. The vent was first mentioned by Geikie (1869), and later briefly referred to by Burns (1888), Smith (1895) and Boyle (1908). Tyrrell (1920) was the first to publish a detailed description of its structure and petrography, and this was later augmented by Eyles (1929). The Heads of Ayr vent is emplaced in gently-dipping sediments belonging to the Cementstone Group of Lower Carboniferous age. It has no large plug intrusion and, apart from a few small monchiquitic basalt bosses, is composed entirely of pyroclastic rocks which are bedded towards the west and imbedded towards the east. This spatial distinction between the two types of pyroclastic deposit is not found in most other Lower Carboniferous vents, perhaps, in part due to poorer exposures of them. The detailed field survey was carried out using enlarged maps of the coastal strip along Heads of Ayr, made from aerial photographs on a scale of 1:1250. It was found possible to trace directly from the photographs many of the structural features of the coast, especially the folding in the bedded pyroclastic rocks of the western end. II. STRUCTURE The vent is naturally divisible into an eastern part and a western part separated by the central recess. These divisions which were This 250-word extract was created in the absence of an abstract The author wishes to acknowledge the advice of colleagues in the Department of Geology, University of Glasgow, and to thank Professor T. Neville George and Dr. D. S. Weedon for their encouragement in the present work and for their critical reading of the manuscript.