SKETCH OF THE GEOLOGY OF DERBYSHIRE. 23 
We return now to the investigation of the position of the beds 
below the new red sandstone, which we broke off in order to describe 
that formation, but, instead of confining ourselves to the S. border 
of the coal-field, we will take the whole of 8. Derbyshire. It is evi- 
dent that, beneath the new red sandstone in the whole of the S. of 
Derbyshire, some part or other of the carboniferous system lies con- 
cealed, because those rocks, as they pass under it on the one hand 
along its northern border, reappear from under it again to the S. in 
Leicestershire. It remains for us to discover under what part of 
this new red sandstone there is a probability of finding the upper 
part of the carboniferous system, or the true coal measures. If we 
begin at Wirksworth, we can trace the limestone shale down to 
Ideridge Hay, from whence we may walk on it, by Biggin and Ag- 
nis Meadow, to Ashbourne Green on the one hand, and by Whidley 
and Milford to Breadsall on the other. Everywhere it passes to the 
S. under the new red sandstone, from beneath which it peeps out at 
two detached places, near Langley and at Wild Park, near Brails- 
ford. We may, then, be perfectly certain that, in all the country 
bounded by lines drawn through Wirksworth, Ashbourne, and 
Derby, there is not the most remote probability of coal being got.* 
If we attend to the position of the limestone shale at Langley and 
Ashbourne Green, we shall see it rising to the S.W. which would 
induce us to expect to find lower rather than superior rocks in that di- 
rection, which expectation is remarkably confirmed by the existence of 
a knob of mountain limestone, which peers above the new red sand- 
stone at Birchwood Park, about five miles S. of Ashbourne. This is 
a slight elevation, about 300 yards long and 150 broad, and consists 
of thick beds of mountain limestone, which dip in every direction 
from a central point, at an angle of 45°. It is surrounded on all 
sides by new red sandstone, and is evidently the top of a conical hill, 
like Crich, except that it springs from a lower level, and according- 
ly is almost entirely concealed by the red sandstone, which spreads 
around it. Further S. about Cubley, are some beds of gritstone, 
which may possibly be millstone grit, but which I suspect to be hard 
* Some persons, deceived by the resemblance of the limestone shale to 
coal measures, and by the occurrence of nodules of coal in a diluvial clay near 
Biggin, have been induced to sink and bore for coal between Ashbourne and 
Turnditch—an absurdity, from the expense and disappointment attendant 
on which the slightest knowledge of the structure of the district would have 
saved them, and which sufficiently shows the want of a greater spread of a 
correct geological knowledge. 
