HUDLESTON : EXCUKSION. 
119 
some of the red colouring to a lower marl now removed. In many 
parts of the Nidd valley the stratum of grit in actual conjunction 
with the Magnesian Limestone is often less highly coloured than 
the bed below. There can be very little doubt that much of the 
red colour of the Plomptou Grits is due to the quantity of red 
felspar which they contain, so that possibly the principal causes 
were pre-existent within the rock itself. 
The fossiliferous horizon known as the Ca^^ton Gill beds, (c of 
the diagram. Fig. 1 ), is seen on both sides of the Harrogate anti- 
clinal. Productus semireticulatus is the most abundant fossil ; 
Streiytorhyiichus crenistria is fairly plentiful, as also a very pretty 
Fenestella ; the joints of Encrinites are very abundant. 
Kinder-Grits. — The base of the Millstone Grits consists of 
three thick grit beds associated with still thicker shales. Some of 
these grits have been extensively used for building stone at 
Harrogate, but they are very porous. Though usally pretty 
free from strong colours, these beds are occasionally very purple, 
though exposure soon removes the tint. The outliers of the Mill- 
stone Grit Series in Craven mostly belong to this section 
YOREDALE Rocks. — This is a group established by Phillips 
for a variable series of beds between the Carboniferous or Scar 
Limestone of Craven, and the Millstone Grit. It is well developed 
in Craven and throughout the west, consisting of shales, lime- 
stones, and peculiar grits, often calciferous. In the bed of Hodder, 
Yoredale Shales, with their limestones and layers of ironstone, 
give rise to springs containing sulphuretted hydrogen. In Bolland 
Forest these shales are dark and full of molluscan and fish remains. 
Near Skipton the Yoredale Rocks consist of calcareous shales 
and limestones with many fossils, the beds sometimes being of a 
ferruginous and bituminous character ; sulphur springs occur there 
in a position somewhat analogous to those at Harrogate. The 
altitude of the Yoredale Rocks at the latter place may be gathered 
from the diagram. PI. IV, Fig. 1. Very little is known about the 
shales of this group, but the Harrogate roadstone (a of the dia- 
