SIMPSON I STRATA AND DEPOSITION OF THE MILLSTONE GRITS. 413 
Bank, and Harewood Park. At Harewood Castle it makes a curve 
northwards, thence dips to the east and south-east, disappearing 
under the Permian Limestone at East Keswick. 
The only remaining member of the series necessitating a short 
description is the Rough Rock, the uppermost bed of the Millstone 
Grits. This is naturally found encircling, as it immediately underlies, 
the Coal Measures from the southern boundaries of Yorkshire with 
Derbyshire, northward and westward, near Huddersfield and Halifax, 
and thence eastward a little north of Leeds, finally disappearing 
under the Permian escarpment. It nowhere attains a greater breadth 
of outcrop than four or five miles. 
Halifax is built on the top of this rock, the rise from the 
Station westward being practically on its dip slope. From the 
heights above the town, westward, it has been denuded until near 
Mount Tabor the flag rock below is quarried at the surface. This 
Rough Rock and its accompanying flag rock are extensively quarried 
along their outcrop for building and paving stones. 
Lithologically this Rough Rock may be termed a coarse, gritty, 
Jelspathic sandstone, with frequent pebbles of vein quartz and 
occasionally of felspar, but generally consisting of rough, angular 
grains of quartz in a matrix of felspar. It weathers on exposure, 
the felspar decomposing quickly under sub-aerial influences, and 
forms picturesque crags on the heights above the valleys. The 
Rough Rock may have about an average thickness of 80 to 100 feet, 
or with its accompanying flags of nearly 150 feet. 
The peculiarity of this rock is its persistence over extensive 
areas, both in thickness and lithological characters. Although it 
extends over hundreds of square miles, it is fairly uniform in thick- 
ness throughout, and the cases where it becomes finely-grained or 
thins away are few and far between. It is difficult to realise how 
such a result could have been brought about by ordinary stream, 
estuarine, or littoral conditions, or even to explain how the constituent 
quartz grains are so angular and crystalline, showing frequently few 
traces of the necessary attrition, whilst at the same time the enclosed 
vein quartz pebbles are generally rounded or sub-angular. 
These are problems necessitating consideration of the probable 
