Prof. T. G. Bonney—Pebbles in the Bunter Beds. 405 
They seem to consist almost wholly of grains of quartz. which are 
very closely agglutinated, so as to give an unusually compact texture 
to the rock, and be with difficulty visible to the eye. The fracture 
is clean and subconchoidal, and the outside of the pebble quite 
smooth. The colour varies; there are many shades of grey, from 
almost white to a sort of dark purplish, and occasionally a peculiar 
liver colour. Pebbles also of white vein quartz are common, with 
hard grits and quartzites rather different from the above, and other 
rocks in small numbers, some of which will presently be noticed. 
Professor Hull pointed out some years since that the quartzite 
pebbles must have been derived from Scotland,! and it was a natural 
inference to refer them to the great mass of that rock which is so 
well developed on or near to the north-western coast. During my 
visit to Ross-shire last summer, I examined the quartzite in the 
vicinity of Loch Maree, and saw either in boulders or in sifu most 
of the varieties which occur in Staffordshire, so far as the unaided 
eye could identify them. The liver-coloured quartzite alone was 
wanting. J had three microscopic sections prepared from Ross-shire 
quartzites (white and grey), and compared them with two from 
Bunter pebbles (grey and liver- coloured ) already in my collection. 
The former consist almost wholly of grains of quartz, agglutinated 
together as is usual in highly-altered quartzites. These grains often 
contain many very minute inclosures, some apparently exceedingly 
small cavities, others specks of opacite, ferrite, etc. They frequently 
have a somewhat linear arrangement. There are also present 
occasional fragments of a very fine-grained quartzite, and of felspar, 
and specks of a greenish micaceous, chloritic or hornblendic mineral. 
The felspar is often banded, some with a wavy or cross-hatched 
structure much resembling that of microcline. All the above also 
occur in the Torridon sandstone; and the quartz and the felspar of 
the Hebridean gneiss, from which its materials have undoubtedly been 
derived, frequently exhibit these characteristics. Now in the slides 
from the Bunter conglomerate we find a similar structure; the 
quartz with similar inclosures, occasional grains of similar felspar ; 
of a fine quartzite, and specks of the same greenish mineral. I can 
see no distinction whatever between the slides from the grey Bunter 
pebble and those from Ross-shire, and that from the liver-coloured 
pebble has only varietal differences. 
Further, it occurred to me when in Ross-shire that if the Bunter 
conglomerate were in great part derived from North-west Scotland, 
one “might hope to find in it specimens of the harder varieties of the 
Torridon sandstone. On my next visit to Staffordshire I found 
that pebbles bearing a close resemblance to it, though with the 
felspar much decomposed, were far from uncommon. ‘Two of the 
best preserved of these have been cut for microscopic examination. 
Now the structure of the Torridon sandstone is rather peculiar. As 
already described in my paper on the vicinity of Loch Maree,* I 
found in it quartz grains like those named above, felspar, “ orthoclase, 
microcline, and plagioclase (? oligoclase),” fragments of fine quartzite 
1 Mem. Geol. Survey, Permian and Trias of Midland Counties, p. 60. 
2 Q.J.G.S. vol. xxxv. p. 98. 
