20 
the millstone grit sequence between masham and great 
whernside. 
by w. s. bisat. 
(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 Wharf edale, 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 Wharf edale. 
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 pro- 
posed 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 Col- 
sterdale 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, near Ripon. 
From the same neighbourhood Dr. Wheelton Hind has since recorded 
{The Naturalist, 1907, pp. 92, 93) a much fuller list, and the mapping 
of the Survey indicated that these beds continued as a fossiliferous 
horizon as far north as Masham. 
The excavation of the trench for the core wall at Leighton 
Reservoir, near Masham, for the Leeds City Council, though un- 
fortunately mainly passing through beds of a barren character, has 
provided an opportunity for making a fairly detailed examination 
of the sequence, the determination of the relative position of the 
two marine bands above alluded to, and the obtaining of satisfactory 
aunal lists therefrom. 
