SKETCH OF THE GEOLOGY OF DERBYSHIRE. 7 
formation of the valley. Of this cireumstance, Monk’s Dale, the 
valley of the Wye in what are called Miller’s and Mousal Dales, 
Lathkill Dale, and Bousal Dale, are admirable examples. One of 
the most interesting circumstances respecting the faults is their con- 
nection with the mineral veins. All the principal lead veins in Der- 
byshire are connected with faults, which run parallel to them at a 
little distance; and as a general rule the vein is on the upcast side 
of the fault. The direction of the veins, moreover, is the same with 
that of the faults, one set running N. and S. the other E. and W.— 
While, however, the principal faults run N. and S. the most regular 
and continuous veins have an E. and W. direction. Some of the E. 
and W. veins have been traced for many miles without any real ter- 
mination having been reached. Of these, the principal are the Yoke- 
cliff, running through Wirksworth ; the Longrake, whose line passes 
S. of Haddon Hall and Mony Ash, and which has been traced into 
Staffordshire ; the Mochsha vein, S. of Bakewell; the Deep Rake 
of Longstone Edge; and the High Rake, the Moss Rake, and the 
Dritton vein, between Tideswell and Castleton. The E. and W. 
veins are generally comparatively narrow, but preserve their width 
throughout their course, and contain a great quantity of ore. The 
N. and S. veins, on the contrary, are more irregular, sometimes widen- 
ing to three or four yards, and then closing, and apparently, perhaps, 
ending, again to open out in another part of their course. Their 
contents, too, are very irregular, being sometimes very rich, and at 
others containing nothing but spar, or not unfrequently fragments of 
rock and broken rubbish, in which merely detached pieces of ore can 
be discovered. To all these evidences of mechanical origin it may be 
added that a vein is itself sometimes a fault, the beds on opposite 
sides of it being shifted from their original common level. 
All these facts accord very well with the theoretical results deduced 
by Mr. Hopkins* by mathematical analysis, from the examination of 
the problem “ What would be the effect of the action of an elevating 
expansive force upon a homogeneous mass of rock, of indefinite thick- 
ness and longitudinal extent, and bounded laterally by parallel lines.” 
He has shown that this effect would be the production of great lon- 
gitudinal fissures running parallel to each other in straight lines, and 
having others at right angles to them. The direction of these sys- 
tems of fissures would be determined by the directions of the princi- 
pal tensions of the mass. That the principal fissures would be at 
* See his paper in the Transactions of the Cambridge Philosophical Society. 
