On the Crush-Conglomerates of Argyllshire

Abstract

I. Introductory In a former communication to this Society dealing with the Dalradian schists of Argyllshire, I described a deposit known as the Boulder-bed, which occurs in the Highland Series along a horizon extending from Aberdeenshire to Islay. I pointed out that this abnormal conglomerate owed its origin to aqueous deposition, and supported that contention by showing that, in various localities along its outcrop, it contains boulders of foreign material. At that time, with the exception of the Isle of Man, where the phenomena of crush-conglomerates had been brought to light by the researches of Mr. G. W. Lamplugh, the occurrence of pseudo-conglomerates had not been recorded in Britain. My subsequent work, however, on the Geological Survey in Cornwall, revealed their existence in that county on a large scale; this was described in the Summary of Progress of the Geological Survey for 1899 (pp. 89 et seqq. ), and in a paper read before the Geological Society of Cornwall last November. On continuing my work in the Highlands last summer I was able to show that these structures occur in Scotland among the Dalradian Series, where they bear so marked a resemblance to many portions of the Highland Boulder-bed that they may readily be confounded together, especially as they are both met with on the same horizon. In my above-mentioned communication to this Society, I sought to demonstrate that the typical crystalline schists of the Central Highlands, when followed into the Loch Awe Basin, pass laterally into sediments which are comparatively