Rev. T. G. Bonnoy — Pitchstones and Felsites of Arran. 499 
sandstone with marl partings. I have not attempted to trace tliis 
conglomerate farther north than Eed Hill, four miles and a half from 
Nottingham. It is there seen, however, in a rather different form 
to what I have described it at Nottingham. Mr. Aveline thus re- 
fers to it : — On the east of the road south of Eed Hill may be 
seen some thick beds of very coarse half-consolidated sandstone 
of a yellow and reddish-brown colour, containing pebbles of quartz, 
and on these lie beds of red sandy marl with bands of fine-grained 
yellow sandstone ; the lower coarse beds are the top of the Pebble 
Beds, the others the bottom of the Lower Keuper Sandstone. A 
few small pebbles occur near the bottom of the latter, but there 
is a very apparent difference between the two series of beds.” 
When I first visited this spot, following Aveline, I, too, regarded 
the “ thick beds ” (about four feet thick) as Bunter ; but on a 
second visit, after a long and careful study of the Keuper con- 
glomerate at Nottingham, my suspicions were aroused by the 
striking resemblance between the thick beds studded with quartz- 
pebbles and precisely the same deep-red half-consolidated sandstone 
associated with the Keuper conglomerate, and a removal of the 
Vegetation shrouding the lower part of the section revealed a 
compact ferruginous conglomerate, eight inches thick, below the 
massive bed of sandstone, and separated from the Bunter — a coarse 
yellow sandstone containing scarcely any pebbles — by about twelve 
inches of soft red marl. Of course this coarse red sandstone con- 
taining the quartz -pebbles was mapped as Bunter. 
III. — On Certain Eock-Structures, as Illustrated by Pitch- 
stones and Felsites in Arran. 
By the Rev. T. G. Bonney, M.A., F.G.S. ; 
Fellow and late Tutor of St. John’s College, Cambridge. 
I N a paper read on February 23rd, 1876, before the Geological 
Society of London, 1 I endeavoured to prove that the peculiar 
laminated or fissile structure, common in certain igneous rocks, was 
due to contraction, like the associated ordinary joint-structures. In 
the discussion which followed, an objection was made to my having 
quoted certain phonolites from Auvergne, in support of my theory, 
because it was well known that the fissile structure in the typical 
phonolites of Hungary was due to change in mineral composition, 
and so the result of a banded structure in the rock. That this was 
not the case with those Auvergne phonolites, I had already convinced 
myself by examination, both in the fiehl and with the microscope. 
and I had nowhere asserted that the only way in which rocks could 
become fissile was by the particular cause which I had advanced ; 
for, although I only knew the Hungary rocks from hand- 
specimens, I was aware of a somewhat similar structure in certain 
British rocks. I thought I remembered also one or two cases in 
these where the fissile and the banded structure were co-existent and 
independent, but as tbe criticism came from a quarter not to be 
1 Q. J.G.S. vol. xsxii. p. 140. 
