6 BON KEY : ON THE ORIGIN OF THE BRITISH TRIxVS. 
I now pass on to some lithological details in these deposits 
and take first the most conspicuous, the pebbles in the Bunter 
conglomerate of the northern and southern areas, in both of 
which no small variety of rocks is represented. The majority 
are at least sub-rotund. On Cannock Chase, where I have 
chiefly studied them (though I have sampled other places from 
Birmingham to Liverpool), the pebbles vary much in size. Those 
from a horsebean to about two inches in diameter are common ; 
very many are between three and four inches ; a few run still 
larger, up to six inches, and occasionally even exceedthat. Several 
kinds of rocks are represented, but in regard to this, as I have 
already discussed the petrography of the pebbles,* I shall restrict 
myself to a brief summary. Vein-quartz and quartzite are 
the most abundant ; the former are usually white, but include, 
though rarely, black tourmaline ; some are brecciated. Quartz- 
ites are numerous and have their grains in a large number of 
cases very perfectly cemented. They vary in colour from 
almost white to a dark tint ; some are reddish, and the char- 
acteristic liver-coloured variety is not rare ; sometimes they 
are speckled with red felspar and thus graduate into a rock 
exactly resembling the noted Torridon sandstone. Pebbly 
quartzites also occur, and others shade off into hard sandstones, 
some of which are fossiliferous. Various mudstones, to use 
an inclusive term, are also present. Pebbles varying from 
dark green to almost black in colour are not uncommon. These 
are generally fine grained quartzites, darkened by interstitial 
chlorite, tourmaline, or iron oxide, some of the most compact 
proving to be porcellanites or cherts, the latter occasionally 
containing radiolaria. Chert also occurs with the well-known 
casts o^ crinoid stems, and limestone with characteristic Lower 
Carboniferous fossils. Neither are common, though the latter 
is perhaps a little more so towards the base of the pebble beds, 
and has recently been found rather more abundantly in one of 
the pits on the Satnall Hills, between Rugeley and Stafford. 
The fossils, however, which have attracted most notice 
occur in the quartzites. In that large compact group, mentioned 
above, we find only a very few annelid tubes, often rather large ; 
* Quart. Jour. G«ol. Soc, Ivi. (1900), p. 287. 
