SIMPSON : STRATA AND DEPOSITION OF THE MILLSTONE GRITS. 409 
Further north, towards Keighley and Skipton, the beds classed 
as Third Grits are 1500 feet thick, with six sandstones, including 
the Addingham Edge Rock. Seeing there is really no consistent 
datum Hue between the Hough Rock and the Kinderscout that can 
be followed with any real accuracy, would it not be much better if we 
ceased to attempt any such arbitrary classification, merely calling all 
between the two, Middle Grits '. 
I should scarcely have dared to advocate this myself, although 
I have many times felt the difficulty, had I not since found that so 
eminent an authority as Professor Green, in the " Memoirs of the 
Yorkshire Coal Field," finds himself constrained to recommend this 
simpler classification. 
They would thus be divided so far as the Derbyshire, Lancashire 
and Yorkshire areas are concerned, as follows : 
1. Rough Rock or Topmost Grit. 
2. Shales. 
4. Shales. 
Kinderscout or Lowest Grits. 
•a, All below the rough conglomeratic and characteristic Kinderscout 
would then be Yoredales ; all above the persistent and easily recog- 
nisable Rough or Top Grit, Coal Measures. 
With these two well recognised datum lines bounding the series, 
and acknowledging the inconstancy of intermediate beds we may, I 
think, rest content to class them generally, however we may do locally, 
as Middle Grits. 
In attempting to grasp the sequence and significance of the 
various beds of the Grit series, we must be prepared for great varia- 
tions and inconstancy ; with the exception, perhaps, of the Rough 
Rock at the top, and, in part, the Kinderscout at the base, nothing is 
so constant as their inconstancy. The sandstones are frequently 
lenticular beds, laid down in hollows and depressions, very variable 
in thickness, appearing, thinning out, and giving place to shales, or 
thickening into several beds with shale partings, within very short 
3. Middle Grits \ 
A group of Sandstones, Gritstones, and Shales, 
very variable in numbers, thickness, and 
character of the Sandy Beds. 
