(Read Sept. 20th, 1913). The district in which the rocks under discussion are situated is bounded on the N.W. by Coverdale, east by the Valley of the Ure, west by Wharfedale, S.E. by the watershed dividing the Burn and Laver valleys, and on the S.W. by an arbitrary line running due west, from Ramsgill into Wharfedale. The whole of the Millstone Grit sequence is not seen in this area, beds which have been referred to the top of the Third Grits being the highest that have escaped denudation. It is of course well known that the succession consists of the usual alternations of grits, sandstones and shales, but owing to the variation horizontally and general similarity of the sandstone and grit bands, it does not appear possible or useful to attempt any division of the series based on the occurrence of grit or sandstone beds at varying horizons. Marine fossils occur at two well-defined horizons, and it is proposed to make use of these two bands as a basis for the subdivision of the sequence. Phillips in his “ Geology of the Mountain Limestone District ” (pp. 209–212) published in 1836, records five marine fossils from Colsterdale on the authority of Danby. The Rev. J. S Tute recorded from the neighbourhood of Ripon (Proc. Yorks. Geol. Socy., 1867 and 1886), a list of marine fossils from an horizon in the Third Grits which he termed the Cayton Gill Beds on account of their being well exposed in Cayton Gill, ...