THE MILLSTONE GRIT AND YOREDALE ROCKS OF NIDDERDALE.

Abstract

I. INTRODUCTION. Nidderdale lies almost entirely in the Millstone Grit country, but in the upper reaches, limestone appears in several small inliers, which are named on the accompanying map. (Plate xix.) At Limley a considerable thickness of massive limestone is exposed, elsewhere limestones and interbedded shales are seen in the bottom of the valley. The limestones have long been known to belong to some part of the Yoredale sequence, but their precise horizon has not previously been ascertained. The Millstone Grit consists of the usual variable series of grits, sandstones, shales, and thin coal seams, and extends from the Basement or Bearing Grit of Grassington Moor to the Brimham Grits at the top of the series, the total thickness being about 1,650 feet. The Brimham Grits, formerly considered to be part of the Third Grit Series, have been correlated by Mr. W. S. Bisat with the Kinderscout Grit and Shale Grit of Derbyshire. In this area, therefore, attention is confined to the lower part of the Grit sequence; the beds above the Kinderscout Grit, which occur in the adjoining parts of Yorkshire and Lancashire, being absent. Two marine horizons : the Colsterdale Marine Band (the “Tesselated Limestone.” of the Geological Survey), and the Cayton Gill Beds, are known; and were mapped by the Survey over a wide area. In the autumn of 1922, Mr. Bisat directed the writer’s attention to the important section which would be exposed in the excavations for the dam of the new reservoir at Scar House.