Intrusive Masses of Boulder-Clay

Abstract

THE letter of Messrs. Graham Officer and Lewis Balfour upon the glacial deposits of Bacchus Marsh suggests the desirability of uttering a word of caution against the assumption that boulder clay intercalated between two beds of rock is necessarily of intermediate age. I have repeatedly observed intrusions of boulder clay into the triassic sandstones of Lancashire and Cheshire, but never so striking an example as that described by Mr. Arthur R. Dwerryhouse in the current number of the Glacialists' Magazine. In his paper and the accompanying plate he shows how a series of glacial and triassic deposits were displayed in a trench in such a way as to give the impression that they were interbedded, sandstone being both below and above the glacial deposits. A minute examination established the fact that the drift deposits had been thrust in amongst the older rocks along a line of weakness due to the presence of a bed of marl. The intrusion had penetrated to a distance of fifty yards from the outcrop of the marl-bed.