99 THE ANCIENT VOLCANOES OF DERBYSHIRE. 
(9) That a vast amount of work remains to be done in determining 
the details of the general structure of the volcanic district, 
and the constitution of the different varieties of deposits. 
I should mention here that since the date of Geikie’s visit Mr. 
Bemrose has been steadily working at the problem, and there is 
little doubt that we shall before very long be furnished with a full 
narrative of the history of the Derbyshire voleanoes. 
Having thus traced an outline of what is known of this inter- 
esting chapter in local geology, it will be profitable now to make 
some general remarks on a few of the more striking features. 
Within the limits of this paper it is, of course, impossible to give 
minute details of any one locality, or even to make reference to all 
places of interest. It must suffice to deal briefly with the chief 
typical phenomena in a general manner. 
Selecting first a feature that is perhaps more apparent than any 
other, we will endeavour to obtain some idea of the nature of the 
Vents; and I propose dealing with two instances with which I am 
well acquainted, viz., those of Grange Mill and Bonsall. Before 
doing so, however, let me draw your attention to the geological map 
of Derbyshire. On this I have marked by a cross the positions of 
the thoroughly authenticated examples of volcanic vents. You will 
notice that the most northerly vent is in the neighbourhood of 
Castleton, and it is not far from the entrance to the Speedwell 
Cavern. The most southerly, and also at the same time the most 
recent, is at Kniveton, where there occurs an inlier of the Mountain 
Limestone, with Yoredale Shales adjacent. The other vents lie 
between Castleton and Kniveton, at Grange Mill, Hopton and 
Bonsall respectively. 
The Grance Mitt Vents lie about five miles to the west of 
Matlock Bath, at the far extremity of that beautiful valley, the Via 
Gellia. They lie on the right of the road to Winster, and may be 
seen immediately after passing the Holly Bush Inn. The Winster 
