THE ANCIENT VOLCANOES OF DERBYSHIRE, 104 
metamorphosed limestones in the neighbourhood of the vent. These 
do not appear to have been changed by the same agencies which in 
other districts have converted the limestone into marble, for in this 
case the limestones have been altered into a substance which is so 
siliceous as to be described as a quartzose rock. Large masses of 
these silicified limestones are to be found in the adjacent fields, and 
small pieces in the walls.» It would almost appear as if the limestone 
had been locally exposed to the action of intensely heated water 
holding large quantities of silica in solution, a feature not uncommon 
in present-day volcanic districts in various parts of the world. 
From the remarks I have made, it will be seen that the Ember 
Lane Vent differs materially from those at Grange Mill. The 
agglomerates are strikingly unlike, and, while we have no lava-flows 
at the latter place, there is distinct evidence of a thick out-pouring 
between Bonsall and Masson, in places showing fluxion-structure, 
and scoriaceous surface formation as marked as if the volcanic out- 
bursts had occurred not millions of years ago but only a few cen- 
turies. The general nature of this deposit indicates that it was laid 
down partly on the surface of the ground near the sea-level, and 
partly on the fioor of the sea. 
The other vents, viz: those at Castleton, Hopton, and Kniveton, 
all possess features of interest in common with those I have described, 
as well as certain characteristics distinctive of each, which cannot be 
entered upon here. 
It should be remembered that those mentioned are merely such 
as have been so far discovered. In all probability several others exist, 
but they have not yet been detected. The possibility of their conceal- 
ment below other deposits is well illustrated by the accompanying 
diagram. And that such hidden vents do occur is suggested in certain 
localities where mining operations have revealed such a great thick- 
ness of igneous rocks as to preclude the idea of their being mere lava- 
streams. At Tideswell Moor, for instance, near Peak Forest Village, 
a shaft has been sunk to a depth of over 600 feet through solid toad- 
