416 Walter Keeping—The Upware and Potton Pebble-beds. 
Hiilleflinta). These Lydian stones are often banded by zones of 
different colour, texture, and hardness. 
4. Larger pebbles (7.e. diameter more than an inch). These are 
much rarer, probably not more than one per cent. of the whole. The 
following have been collected at Potton, and may now be seen in the 
Woodwardian Museum. 
a. Vein-quartz.—These are the most common, five or six of them 
being found to one of the rest. They are fairly well rounded, and, 
as arule, do not exceed three inches in diameter. Traces of metallic 
ores are sometimes seen in them. 
b. Fragments of hard vein-breecia ; slaty and quartzose varieties, 
sometimes with geodic cavities. 
c. Quartzite. —A very compact, hard, light-coloured variety, much 
resembling that from the Bunter conglomerates. These do not 
attain quite the size of the others. 
d. An angular fragment of white saccharoidal quartzite measuring 
4 x 24 x 24 inches, spotted with pale pink felspar crystals, and 
imperfectly laminated with layers of white mica. 
e. One specimen only. A subangular, dark-coloured pebble of 
fine-grained, altered grit, with veiny patches of quartz. 
f. Altered Grit.—A fine quartzo-felspathic grit of dark colour with 
small black specks—much resembling some of the grit in the Lower 
Cambrians of Wales. ‘Two specimens found; the largest is a long 
pebble with the greatest diameter about 84 inches. Prof. Bonney 
states that in his specimen are several groups of minute belonites 
much resembling tourmaline. 
g. Hard sandstone so indurated as to be almost a quartzite; light 
yellowish or whitish colour. These attain a somewhat greater size 
than (a); they have evidently been a good deal rolled, but are more 
irregular in shape. They appear identical with a rock common in 
the Cambridgeshire drift, which comes, I believe, from the Carbon- 
iferous series. 
h. Indurated shale and Lydian stone. — Most of the fragments 
which have hitherto been designated Lydian stone are, I believe, 
more correctly chert. We have, however, met with some which 
appear properly to belong to this group of highly altered rocks. 
7. Well-rounded oval pebbles of pale yellow, fine-grained argil- 
laceous sandstone, sometimes micaceous and thinly laminated. 
k. An irregular, oblong fragment of Cambrian or Silurian pale slate 
measuring 24 x 14 x # inches, its contours sharply angular and 
joint-hacked. It is made up of two distinct zones of rock :—(1), a 
pale olive-coloured soft shaly rock, really a slate, splitting at a 
high angle across the plane of the fossils; and (2), a half-inch of 
fine-grained felspathic, ash-like grit crowded with fossils. The 
specimen has now been broken up and Iam able to identify from it— 
Favosites fibrosus, var. ramulosus, Phillips. 
Orthis elegantula, Dalman. 
»,  testudinaria, Dalman ? 
»,  biforata, Schlotheim. 5 
Strophomena, sp. (same as one from the Dalquorhan sandstones; 0/404, of the 
Cambridge Catalogue). 
