Walter Keeping—The Upware and Potton Pebble-beds. 415 
ticularly indebted for the generous gift of his notes already written 
upon this subject. 
The Potton and Upware Nodule beds have been already described 
by Professors Bonney and Seeley, Mr. Teall and Mr. Walker, and it 
is sufficient here to state that the deposit is a pebble bed or (when 
hardened by carbonate of lime or limonite) conglomerate, with a 
matrix of quartz sand, usually ferruginous, sometimes shelly and 
calcareous. — 
The great majority of the pebbles are the phosphatic nodules or 
‘coprolites ’ themselves, for the extraction of which the bed has been 
worked for the last ten or twelve years. These are of various ages, 
principally Upper Jurassic, but some of them are fragments of older 
Neocomians which were saturated with phosphate in the Upper 
Neocomian sea; none of them are proper to the bed itself. But 
besides these there is a scattering of other pebbles and rock-frag- 
ments, devoid of phosphate, which in the course of the workings are 
separated out by hand picking and thrown aside; and it is to these, 
as being but little known, though of peculiar interest, that we would 
now call particular attention. The following are found :— 
1. Fragments of older Cretaceous rocks; mostly a dark-coloured, 
nearly black, ferruginous grit rock ' occurring in irregular fragments 
often as much as three inches across. It contains numerous casts 
of Neocomian fossils, Cucullea donningtonensis (MS.), Cardium sub- 
hillanum, ete. Rolled fragments of the Wealden Endogenites are also 
not infrequent in the Potton sands, and I have lately found it at 
Upware. 
2. Pebbles from various Jurassic rocks, such as rolled fragments 
of limestone and chert, which have doubtless come from many of 
the Lower Oolites; argillaceous limestone, which may have been 
derived from concretions in Kimmeridge-clay or Oxford-clay, or even 
from the Lower Lias; and arenaceous rocks such as occur sometimes 
in the Lower Oolites of the Midlands. 
One large pebble of pale yellow sandstone (3 inches diam.) has 
yielded a few fossils ; namely, a mytiloid shell, and a transverse 
bivalve of doubtful affinities. The age of the rock is uncertain, but 
the balance of opinion would refer it to some part of the Jurassic 
period. Fragments of chert from these rocks are described below. 
Besides these however, we find the following, obviously from a 
more ancient source :— 
3. Small pebbles from about the size of a filbert downwards to a 
hempseed. These are abundant, so that often a dozen or more may 
be detected upon the face of a hand-lump of the phosphate rock. 
Quartz, apparently vein-quartz, is not uncommon; but the majority 
are angular or subangular fragments of hard, highly siliceous, fine- 
grained rocks, mostly dark coloured, many of which are simply chert, 
resembling that common in the Mountain Limestones of Derbyshire, 
the rest being highly indurated argillites (Lydian stone and 
1 This rock, and its fossils, are described more fully in another work on ‘‘ The 
Fossils and Paleontological Affinities of the Neocomian Deposits of Upware and Brick- 
hill,”” not yet published. 
