ON THE RHYTHMIC SUCCESSION OF THE YOREDALE SERIES IN WENSLEYDALE

Abstract

The alternations of sandstones, shales and limestones which occur between the Great Scar Limestone and the Millstone Grit in the West Riding of Yorkshire form a distinct facies of the upper part of the Lower Carboniferous, and have long been known as the Yoredale Series. This name was given to them by Phillips *, who first described them in detail, and took as his type section that so well exposed in Wensleydale. He chose, to use his own words, “as a general standard of reference for this complex series of rocks that district where this complexity is greatest. The upper end of Wensleydale was, therefore, adopted.” Later he records the fact that other sections were very satisfactorily in accordance with the Wensleydale section and “ justifies the use of that as a common standard of reference.” Phillips regarded the shale which lies immediately above the Gayle Limestone as marking a distinct change in the physical conditions under which the beds were accumulating in this area, and he, therefore, commenced the Yoredale Series with this shale. The change, however, from normal limestone to Yoredale conditions occurs before this. Shales, notably the Gayle shale, occur near the top of the massive limestone, together with algal horizons, which are very characteristic of Yoredale conditions of sedimentation. One such horizon, in particular occurs 49ft. below the top of the Great Scar Limestone, and this horizon, the Girvanella Bed, is taken, for the purposes of this paper, as the base of the Yoredale Series. A …