216 
secretary's report, 1906. 
these igneous rocks were ejected, and at a much more recent date 
(probably Eocene) these series of rocks were invaded by intrusive 
sills of doleritic rock. The lavas are full of steam holes, which are 
often found filled with crystalline material, which forms almond- 
shaped bodies (amygdaloids). Under Raven Crag the Carboni- 
ferous Limestone is found including small crystals of iron 
pyrites, and the decomposed upper layer of the tuff contains 
small crystals of selenite. The limestones seem to have been 
laid down in shallow water, and the eruptions which gave vent 
to the lava (toadstone) and the ashes (tuff) were probably sub- 
marine. The limestones overlaid by the subsequent intrusive 
sills are burnt and converted into marble to a depth of ten feet 
or so. When, however, the sill overlies a lava- flow the underlying 
limestone is not marmorized. Where the sill lies on a bed of 
tuff it is baked and a columnar structure is produced. Mr. 
Bemrose also descibed the route to be covered by Saturday's 
excursion. 
On Saturday the party Avent by wagonette to Cromford, 
through the lovely limestone gorge of the Derwent. Willersley 
Hall, the home of the Arkwrights, and the mills where Sir 
Richard carried on his celebrated manufacturing processes, were 
noted with interest. At Cromford Station the Limestone Shales 
above the main limestone were examined, and then a visit was 
paid to the Black Rocks. These well-known picturesque rocks 
form part of an escarpment of the lower or Kinderscout 
beds of the Millstone Grit. They are fine specimens of grit 
weathering, one projecting mass in particular resembling a 
gigantic animal. 
The route was continued through Middleton, the neighbour- 
hood of which appears to be honeycombed with lead workings, 
and on, up the Via Gellia, to Grange Mills, near which several 
sections in the volcanic rocks of the Carboniferous series were 
examined. The sections show a couple of volcanic necks, which 
are the filled-up vents from which the lavas and tuffs were 
ejected that form the toadstone and ash beds of the neighbour- 
hood. The volcanic ashes lie in a semicircular belt round the 
necks and are part of the volcanic cone dissected. The bed of 
limestone immediately above the breccia of the neck is full 
