﻿Rev. T. G. Bonney — Pitchsto7ies and Fehites of Arran. 499 



sandstone with marl partings. I have not attempted to trace this 

 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 Ked 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 Cektain Eock-Structukes, as Illustkated by Pitch- 

 stones AND FelSITES in AkRAN. 

 By the Eev. T. G. Bonnet, M.A., F.G.S. ; 

 Fellow and late Tutor of St. John's College, Cambridge. 



IN a paper read on February 23rd, 1876, before the Geological 

 Society of London,^ 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 theorj^, 

 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 phonoiites, I had already convinced 

 myself by examination, both in the field and with the microscope. 

 and 1 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 the criticism came from a quarter not to be 



1 Q.J.G.S. vol. xsxii. p. 140. 



