SIMPSON : STRATA AND DEPOSITION OF THE MILLSTONE GRITS. 411 
tions which are evident mostly in the lower members, as the Rough 
Rock was laid upon a comparatively even floor. 
The thickness of the Kinderscout sandstones and shales, then, 
varies most considerably in the different districts from 200 feet or so 
to over 1,000 feet. Between Bam ford Edge and Rood Hill we get an 
average thickness of Kinderscout of 900 feet, with southerly thinning 
away ; west of Halifax and Huddersfield about 350 to 500 feet ; in 
the Keighley and Skipton districts probably over 1,200 feet. 
Lithologically the Kinderscout grit is generally exceedingly coarse 
and very massive, frequently quite conglomeratic, with pebbles of vein 
quartz, rounded or sub-angular, of all sizes up to nearly two inches in 
diameter ; there are occasional beds of flagstone, and where it is most 
largely developed it is in two or more beds, with shale partings. 
This grit is well exposed in the valleys west of Halifax, and along 
the summit of the Pennine Chain, on the Cononley and Skipton 
Moors, and will be familiar to all, as the rock of the Strid at Bolton 
Woods. 
It is, however, in the Middle Grits, known generally as the 
Second and Third Grits, that we meet with most variation. They 
are the most inconstant members of the series, and it is in the 
difficulty of properly correlating these that I should advocate the 
simpler classification of Middle Grits. 
In Derbyshire, as I said, there are two clear, distinct beds of 
sandstones between the Rough Rock and the Kinderscout. In York- 
shire this clear division ceases, the uneven bottom of the Kinder- 
scout had not yet been levelled up, and the Middle series thicken 
out, and occur as large lenticular beds in the old hollows. 
In the Halifax district, if we include the flag rock at the base of 
the Rough Rock, which is usually classed as the Second Grit, we get 
five fairly important beds to represent the two of Derbyshire, whilst at 
Keighley they have further increased to six or seven. The sand- 
stones are, in our district, usually less gritty and finer than either 
the Kinderscout or Rough Rock, though still very variable in litho- 
logical character. In the shales of this Middle series are three or 
four inconstant, unimportant coal bands, thin and poor in quality, 
and of small commercial value, though they have been occasionally 
I 
