CHAP. XXIX 
THE DERBYSHIRE TOADS TONES 
17 
lava or pumice, and encloses large and small rounded blocks oi finely 
cellular basalt and pieces of limestone. The rock is unstratified, and in all 
respects resembles that of ordinary Carboniferous necks in Scotland. Its 
relations to the Yoredale rocks are laid bare in the channels of the 
streamlets. There the shales and thin limestones may be seen much broken 
and plicated, their curved and fractured ends striking directly at the agglo- 
merate. They may be traced to within a yard of the agglomerate. On the 
Geological Survey map the igneous rock is represented as bounded by two 
parallel faults. But I hardly think that this explanation suffices to account 
for the relations of the rocks and their remarkable boundary-line, which 
seems to me to be undoubtedly the wall of a volcanic vent. To the east of 
the streams, another mass of agglomerate may mark another neck, while to 
the north, a third detached area of the same kind of rock, rising among the 
limestones, may be regarded as likewise a distinct mass. At this locality, 
therefore, there are two, possibly three, vents. One of these, from the way 
in which it cuts across the Yoredale shales and limestones, is to be assigned 
to a time later than the older part of the Yoredale series, and thus, like the 
Hopton mass, it indicates that in the south of the volcanic area eruptions did 
not cease with the close of the deposition of the thick limestones, but were 
prolonged even into the time of the Yoredale rocks. 
A further proof of the late age of these southern patches of volcanic 
material is shown by two bands of vesicular toadstone in the Yore- 
dale series, a little south from the village of Kniveton. These rocks are 
traced on the Survey Map, and are shown in a diagram in the Memoir, 
where their position is sought to be explained by a system of parallel fault- 
ing . 1 I was able to trace the actual contact of the western band with the 
strata underneath it, and satisfied myself that there is 110 fault at the 
junction. The igneous material is regularly bedded with the Yoredale shales 
and limestones. Either, therefore, these bands are intercalated lava-streams 
or intrusive sills. If mere vesicular structure were enough to distinguish 
true outflowing lavas, then there could be no doubt about these Kniveton 
rocks. But this structure is found in so many Carboniferous sills, 
particularly in those thin sheets which have been injected into coals 
and black shales, that its presence is far from decisive. The vesicles in the 
Kniveton rocks are small and pea-like, tolerably uniform in size and shape, 
and crowded together. They are thus not at all like the irregular cavities 
in the ordinary cellular and scoriaceous lavas of the toadstone series. 
Whether or not the question of their true relations be ever satisfactorily 
settled, these Kniveton bands are certainly younger than the lower portion 
of the Yoredale group. Their evidence thus agrees with that of the southern 
agglomerates in showing that the volcanic activity of this region was con- 
tinued even after the thick calcareous masses of the Carboniferous Limestone 
series had ceased to be deposited. 
Besides the six necks to which I have referred, a rock in Ember Lane, 
above Bonsall, probably belongs to another vent .' 2 It is particularly interesting 
1 Op. cit. p. 87. 2 This is outcrop No. 39 of Mr. Bemrose’s paper, p. 632. 
VOL. II C 
