SKETCH OF THE GEOLOGY OF DERBYSHIRE. i) 
THE LIMESTONE SHALE. 
The E. and W. sides of the limestone district are bounded by a 
narrow valley worn out in the soft beds of the shale, which on the 
one side reposes regularly on the limestone, and on the other rises 
half way up the hills, and supports the millstone grit.—(See sections 
land 2). This valley varies in width from 3m. to 2m. according to 
the greater or less extent to which denuding forces have acted upon 
it and its gritstone covering. Occasionally, however, there is no 
valley, but a hill of shale rising abruptly from the hill of limestone 
on which it rests; or it is not unfrequent to find a hill of shale rising 
out of the valley, and protected by a cupping of millstone grit. It, of 
course, every where partakes of the inclination of the limestone below 
it, and must be affected by the same or similar faults. Where, how- 
_ ever, the solid beds of the limestone have been snapped clean asunder 
by the dislocating force, the softer beds of the shale are often bent 
and contorted in the most singular manner. In these lateral tracts, 
however, the shale seldom shows anything of remarkable interest. 
In the part N. of Castleton, the most remarkable spot in the shale, 
is the well-known hill called Mam Torr, or the Shivering Mountain, 
which is a hill of shale resting upon limestone, and being very preci- 
pitous, especially on one side, the action of the weather has continually 
undermined and worn away the loose and crumbling materials, until 
a great natural excavation has been formed, to which each successive 
winter makes additions, while the ruin lies scattered at its foot. The 
line of hills between Castleton and Eedale consists chiefly of this for- 
mation, whence it stretches away to the N. with many minor corru- 
gations and changes of dip, but on the whole nearly horizontal, form- 
ing, as it were, the base of the country for the support of the masses 
of gritstone. The valleys all cut down deeply into the shale, fre- 
quently exposing faces that exhibit its alternation with, and gradual 
passage into, the millstone grit. If we go to the S. of the limestone 
district, we find the shale spreading out, and occupying nearly all the 
country between Wirksworth, Derby, and Ashbourne, north of’ the 
boundary of the new red sandstone. Over this tract its position is 
remarkable, as it is bent up and down, in every direction, into great 
curves; but the scarcity of natural or artificial sections renders it 
rather difficult to make out. On the E. it may be seen going down 
from Wirksworth, below Ashley Hay and Shottle, to Milford, dipping 
every where to the E. under the gritstone. At Milford its dip is 
VOL. IX., NO. XXV. 2 
