103 THE ANCIENT VOLCANOES OF DERBYSHIRE, 
more conjectural. I am, however, inclined to the former view. For 
instances of modern volcanic phenomena, which support the general 
suggestions here offered, we have only to think of the marine 
volcanoes of the Grecian Archipelago and some of the Pacific Islands. 
Tue Vent at Bonsatt, a village about two miles north-west of 
Cromford, which may also be reached from Matlock Bath by climbing 
over the shoulder of Masson Hill, near the Heights of Abraham, is 
well exposed in Ember Lane, down which one must pass on the 
journey from Matlock to Bonsall. The lower part of the lane—that 
nearest Bonsall—is bounded on each side by walls built almost 
entirely of a very coarse agglomerate, of quite a different character 
to that found at Grange Mill. The peculiar and almost unique 
feature of the Bonsall agglomerate is the presence of a preponder- 
ance of fragments of limestone, most of them quite unaltered by 
heat. Some of the fragments are pebble-like, and would suggest 
either the presence of a sea-beach, or the wearing caused through 
repeated expulsion and attrition by violent contact in the air. Some 
of these pieces are as large as an orange, and they are enveloped in a 
matrix of a chocolate colour, with lapilli of a greenish colour, which 
are often more or less decomposed. At one spot in the lane, on the 
left-hand side going from Bonsall, a section occurs where the rock is 
quite decomposed, the matrix forming a clay-like mass in which the 
nodules of limestone are embedded. Further up the lane the 
character of the deposit changes, for we find ourselves passing over 
a sheet of amygdaloidal and vesicular lava, evidently part of the same 
flow which is found further away on the summit of Masson Hill. 
An examination of the walls bounding the road and the adjacent 
fields shows them to consist largely of both vesicular and amyg- 
daloidal Toadstones, with occasional lumps of dark and very hard 
dolerite, though this variety is met with more frequently nearer to 
Bonsall, and it probably points to the existence of a dyke near at 
hand. A further feature of interest, which ought to be mentioned, 
is the somewhat remarkable occurrence of considerable quantities of 
