The Petrography of the Millstone Grit of Yorkshire

Abstract

The term ‘Millstone Grit’ is applied to a series of beds which attain a thickness of 5500 feet in Lancashire, consisting of conglomerates, grits, sandstones, and shales with occasional thin impure limestones and beds of chert. It occupies a position in the geological sequence between the Yoredale or Pendleside Group and the Coal Measures. For the purposes of this investigation the base of the Millstone Grit in West and North-West Yorkshire has been taken at the base of the Ingleborough Grit, following the precedent of the Geological Survey as pointed out in the Memoir on the Ingleborough District, 1890, pp. 74–75. Since this is a coarse grit, easily traceable on account of its lithological characters and the bold escarpments to which it gives rise, it forms a good datum-line. The top of the series has been taken at the top of the Hough liock, where it can be seen to be overlain by the Lower Coal Measures, as at Whitehall Quarries, Horsforth, near Leeds. However, as no questions of correlation are involved in this work, the exact delimitations of the various beds is a matter of minor importance. The Millstone Grit Series covers an area in Yorkshire alone of no less than 840 square miles, and is important physiographically, as it forms the capping of most of the hills of the Pennine Chain, such as Mickle Fell. Whernsicle, Ingleborough, Penygent, etc., and by its presence there preserves the more easily denuded strata below from a more rapid destruction. Economically the