SKETCH OF THE GEOLOGY OF DERBYSHIRE. 29 
tant change during this period ; and unless the laws of nature were 
very different in those days from what they are at present, which 
we have no right to assume and no reason to believe, we know that 
this must have been a work not of hundreds, scarcely even of thou- 
sands of years. During all this period we have no instance of dis- 
turbances taking place in this district ; an ejection of igneous rock 
over the bed of the sea certainly occurred, but there is no trace of its 
having been accompanied by any violent dislocating force ; there 
are no dykes, no veins even, of solid toadstone running into the lime- 
stone.* After the last of the coal measures were deposited, how- 
ever, this district, in common with all the neighbouring ones, in the 
W. of Europe at least, came to be violently acted upon by upheav- 
ing and dislocating forces. Large portions of the previously level 
bed of the sea were lifted up, many fissures, both large and small, 
were formed in obedience to the mechanical laws, faults and veins 
being their result, and many beds, when not broken through, were 
bent and contorted in various directions, but still, no doubt, under 
the regulation of similar laws. This violent disruption of the bed 
of the sea,t whether it took place suddenly, or, as is to my mind 
more probable, was a comparatively slow and continued operation, 
would no doubt cause great currents to act upon the broken strata ; 
and we find accordingly that great denudation, or washing away, of 
immense quantities of the previously formed beds, has taken place 
either during this period or subsequently, and many of the present 
valleys of the country were certainly begun at this ancient time. 
However long these disturbances may have continued, however, we 
find that at length they nearly or entirely ceased, and that portion 
of the district which was still covered by water again began to de- 
posit new materials. On the E. side of the district there was a sea, 
in which limestone was again deposited, but mixed to a greater or less 
extent with sand and mechanical detritus, and containing also mag- 
nesia. Some parts of it, however, were sufficiently clear for the 
deposition of pure crystalline limestone and the existence of animal 
life, since about Bolsover and near Kirkby, in Ashfield, a few beds 
of carbonate of lime, containing shells, are found ; others, again, 
were agitated by currents sufficiently strong to bring in pebbles of 
* The toadstone clay is frequently found to have come down some dis- 
tance into the lead veins, but that it would do now were a new fissure 
formed. 
+ Or what at least had been the bed of the sea, and was then covered by 
water, either fresh or salt. 
