SKETCH OF THE GEOLOGY OF DERBYSHIRE. 25 
least. Towards the S. we have traced it into Leicestershire ; but 
in this direction it appears to be thinning out, and no doubt shortly 
ends. To the W. it runs some distance into Staffordshire, and in- 
deed all across it into Cheshire, as it may be seen reappearing from 
under the gritstone hills near Congleton. To the N. it passes under 
the shale and gritstone, from beneath which it reappears in Lanca- 
shire and Yorkshire. While to the E. we find it, after passing 
under the shale and gritstone for some miles, reappearing at Crich 
and Ashover without any appearance of diminution, and again pass- 
ing regularly under the coal-field to the E., beneath which it runs 
to an unknown extent ; but, even supposing it to thin out in this 
direction as fast as it does to the S. it must run for some distance 
into Nottinghamshire. The whole of Derbyshire, then, is based on 
mountain limestone, which, after forming the surface of the districts 
before described, sinks down on every.side, and is covered by coating 
after coating of the superior rocks, the limestone shale, the millstone 
grit, and the coal measures. All these are always conformable to 
each other, each dipping (in the same places) in the same direction 
and at the same angle, and being, in fact, only different parts of one 
compact and continuous mass of rocks, all the four insensibly melting, 
as it were, into one another, and forming one whole. Of this whole, 
however, large quantities of the upper parts have, in different 
places, been stripped off, and thus the lower portions are exposed to 
view, and there seems, to a casual observer, to be no connection be- 
tween the two. This stripping off has chiefly taken place in the 
central part of the district, where the greatest amount of upheaving 
force was exerted, and consequently the rocks more shattered and 
rendered an easier prey to the denuding powers, whatever they 
were; while, as the beds sink down on every side, higher and 
higher rocks continually mantle round, and have been preserved, by 
their comparatively slight elevation, from this denuding action. 
Whenever any part, however, of this mass of rocks sinks below a 
certain level, if it be on the outskirt of the district, it is sure to be 
covered by one part or other of the next superior mass of rocks, the 
new red sandstone. These are equally conformable amongst them- 
selves, and equally melt one into another, but the different parts are 
more irregular in their thickness and extent ; so that one sometimes 
thins out and ends altogether, while the rest continue. But if now, 
disregarding the parts of which these two classes of rocks are com- 
posed, we look upon the carboniferous system and the new red sand- 
VOL. IX., NO. XXV. 4 
