CHAP. XXIX 
THE DERBYSHIRE TOADSTONES 
13 
found in a part of the Yoredale group of shales and limestones which form 
the uppermost member of the Carboniferous Limestone of this region. But 
it is not quite clear whether the vesicular diabase found there is inter- 
stratified or intrusive. Certainly no contemporaneous tuffs have yet been 
found among the Yoredale rocks, nor in any higher subdivision of the 
Carboniferous system, though coarse agglomerates marking the position of 
vents do traverse the Yoredale group at Ivniveton. 
It may be remarked that in the district over which the toadstones can 
be seen, two areas are recognizable, in each of which the exposures of the 
igneous rocks are numerous, while between them lies an intervening tract 
wherein there is hardly any visible outcrop of these rocks. The northern 
and much the more extensive area stretches from Castleton to Sheldon, 
while the southern spreads from Winster to Ivniveton. This distribution 
not improbably points to the original position of the vents, and indicates a 
northern more numerous group of volcanic orifices, and a southern tract 
where the vents were fewer, or at least spread their discharges over a more 
limited space. 
3. the VENTS. — It had always appeared to me singular that, in ground 
so deeply trenched by valleys as the toadstone district of Derbyshire, no 
trace had been recognized of any bosses or necks from which these volcanic 
sheets might have been erupted. It is true that in mining operations 
masses of toadstone had been penetrated to a considerable depth without 
their bottom being reached, and the suggestion had been made that in such 
cases a shaft may actually have been sunk on one of the vents through 
which the toadstone came up. 1 One instance in particular was cited where, 
at Black Hillock, on Tideswell Moor, close to Peak Forest Village, a mass 
of toadstone was not cut through, though pierced to a depth of 100 
fathoms. In that neighbourhood, however, several of the sheets of eruptive 
material are probably sills, and the shaft at Black Hillock may have been 
sunk upon the pipe or vein that supplied one or more of these intrusive 
sheets. 
It was therefore with no little interest that I detected a series of 
vents at four separate localities, viz. Castleton, Grange Mill, Hopton, and 
Kniveton Wood. I have no doubt that a more extended search will bring 
others to light. Those observed by me are all filled with coarse agglomerate, 
the blocks in which are mostly composed of different lavas, sometimes with 
the addition of blocks of limestone, while the matrix consists mainly of 
lapilli of basic devitrified glass. 
The most typical examples form a group of two, possibly three, vents 
which rise into two isolated, smooth, grassy dome-shaped hills at Grange 
Mill, five miles west from Matlock Bath. 2 In external form and colour, 
these eminences present a contrast to the scarped slopes of limestone around 
them. They at once recall the contours of many of the volcanic necks in 
Central Scotland. On examination it is found that the material composing 
1 Geol. Surv. Mem. on North Derbyshire, p. 134. 
2 This is Mr. Bemrose’s outcrop, !No. 46, op cit. p. 633. 
