8 
THE CARBONIFEROUS VOLCANOES 
BOOK VI 
stones probably proves that it was intruded before the rocks were much 
disturbed from their original horizontal position. But the manner in which 
the intrusive rock lias been thrust into and has involved the shales and lime- 
stones seems to indicate that these strata had already become consolidated 
and lay under the pressure of a great thickness of superincumbent 
Carboniferous strata. 
In the absence of all certainty on the subject it seems most natural to 
place the Whin Sill provisionally among the Carboniferous volcanic series 
with which petrographically and structurally it has so much in common. 
In Scotland the puy-eruptions continued till the time of the Coal-measures. 
If, before the close of the Carboniferous period, volcanic vents were opened 
somewhere to the east of the coal-fields of Northumberland and Durham, 
they might be accompanied with basic sills injected into the Carboniferous 
Limestone series, which was then lying still approximately horizontal under 
a thickness of from 3500 to 5000 feet of Carboniferous sedimentary deposits. 
These still undiscovered volcanoes seem to have been endowed with even more 
energy than those of Central and Southern Scotland, at least nowhere else 
among the Carboniferous records of Britain is there such a colossal mani- 
festation of subterranean intrusion as the Great Whin Sill. 
2. THE DERBYSHIRE TOADSTONES 
In the absence of any certain evidence that the Whin Sill belongs to 
the Carboniferous period, we must advance southward into the very heart 
of England before any clear vestiges can be found of contemporaneous 
volcanic eruptions among the members of the Carboniferous system. After 
quitting the lavas and tuffs of Roxburghshire and their brief continuations 
across the English border, we do not again meet with any truly bedded 
volcanic rocks in that system until we reach the middle of Derbyshire. In 
this picturesque district, famous for its lead-mines and its mineral waters, 
a feebly developed but interesting group of intercalated lavas, locally 
called “loadstones,” has long been known. There is thus a space of some 
150 miles across which, though the formations are there so fully developed 
and so abundantly trenched by valleys from the top to the bottom of the 
system, no volcanic vents nor any trace of Carboniferous volcanic ejections 
has yet been found. . On the other hand, after the district of the “toadstones ” 
is passed, the Carboniferous rocks are again destitute of any volcanic inter- 
calations across the centre and south-west of England and over Wales, until 
a tei a space of about 150 miles they reappear in Somerset. 
The volcanic group of Derbyshire thus stands out entirely isolated. 
Jing m the Carboniferous Limestone, where that formation is typically 
developed, it presents an admirable example of a thoroughly marine phase 
of volcanic action (Map I.). 
One of the most prominent features in the geology of the centre of 
England is the broad anticlinal fold which brings up the lower portion of 
the Carboniferous system to form the long ridge of the Pennine chain that runs 
