Quartz-Dolerite Pebbles (Whin Sill Type) in the Upper Brockram

Abstract

THE finding of a small pebble of fine-grained quartz-dolerite in an exposure of the Upper Brockram in George Gill, near Appleby, by Professor Arthur Holmes in 1925 and its identification with the rock of the Whin Sill led to the direct establishment of the timeof injection of the Whin Sill and related dykes as post-Carboniferous and pre-Upper Brockram (1928, pp. 532–4). Since 1925 parties of students from the Durham Colleges’ Department of Geology have made each year a careful search for similar pebbles not only in the George Gill exposures but in a number of others in the Brackenber Moor neighbourhood. These efforts have not been rewarded with any success until the present year, when a party under my guidance made a thorough examination of the George Gill Brockram and Mr. A. R. Leathley, of Hatfield College, had the good fortune to hammer out a pebble of doleritic aspect.