200 Prof. T. G. Bonney—Pebbles in the Bunter Beds. 
(for circumstances have not allowed of this) to have made anything 
like a complete collection. Many of my specimens have been 
derived from the broken materials spread upon some roads newly 
made over the portion of the Chase in the vicinity of Rugeley, but 
several of them were obtained in a large pit in the Bunter itself, by 
the side of the railway on the road to Hednesford, and I was able by 
a careful search in it to identify most of the varieties that I had 
collected elsewhere. I cannot say that erratics are absolutely un- 
known in this district, but they are extremely rare, and there is 
practically no danger of making a mistake as to the source of the 
pebbles. These pebbles of felstone (to use an inclusive term) appear 
to be by no means rare. I think one could hardly search a couple 
of square yards of a newly “ metalled” road without picking up a 
fragment. Now and then specimens are found with a dark ground- 
mass, and occasionally one which seems to be an indurated felspathic 
breccia; but in the majority there is a certain common character, 
though there are many varietal differences. These have a compact 
ground-mass, varying from a pale brick-red (the commonest) to some 
tint of pinkish-grey. In this are scattered crystals of felspar, some- 
times as much as 0-4 inch in longer diameter (generally paler in colour 
than the matrix), grains of quartz, and occasional specks of greenish 
or dark-coloured minerals. They are in short a group of porphyritic 
quartz-felsites—the quartz-porphyries of many authors. Not seldom 
a trace of fluidal structure can be detected in the matrix, and occa- 
sionally this is very conspicuous. Vesicles also may now and then be 
noticed. The rock appears usually in very fair preservation, but the 
exterior of the pebbles is generally a little paler than the interior. 
I have examined microscopically ten varieties, but as it would be 
rather wearisome to the reader to describe each specimen in detail, I 
will endeavour to give the general results of my investigation. 
Three of the specimens exhibit a more or less distinct spherulitic 
structure; in the remainder the ground-mass is either minutely 
micro-crystalline or crypto-crystalline, consisting obviously of quartz 
and a felspathic mineral, more or less decomposed and ferrite-stained. 
In one specimen these are associated with microliths of a greenish, 
rather fibrous mineral, which in part is tourmaline, but in part is a 
nearly colourless mica. In two others tourmaline is a constituent of 
the ground-mass ; in these it seems to have replaced a magnesia-iron 
mica, probably biotite, and in one possibly a hornblende. 
The quartz grains are usually rather abundant, and are variable in 
form, even in the same specimen. Sometimes one or more crystalline 
angles are well exhibited, sometimes (and this may be in the same 
grain) the margin is rounded or pierced with inlets of the ground- 
mass, inclosures of which are also common. Cavities are always 
present ; in some more abundantly than others, in one or two slides 
they appear to be empty, in others they contain fluid with bubbles. 
The relative size of these varies considerably, perhaps most com- 
monly they occupy about ith of the cavity, but the difference is 
sometimes considerable even in the same grain—in one such case 
the ratio of the bubbles to the cavity is from 1:10 to 1:5. Talso 
