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738 PROF. J. W. JUDD ON THE NATURE AND RELATIONS OF 
VIL. Tur Neocomran (?) Buns. 
Down to this point the order of succession and the thicknesses of 
the several deposits were precisely such as were anticipated from the 
data already obtained concerning the strata of the London Basin. 
But below the base of the Gault certain rocks of a very remarkable 
and unexpected character were encountered in the Richmond well. 
The ‘“‘junction-bed” at the base of the Gault was found to rest 
directly upon beds of limestone of a somewhat peculiar character. 
The uppermost portion of this limestone was rather sandy in compo- 
sition, and contained some particles of glauconite and a great 
number of brown grains which had the appearance of being formed 
by the decomposition of that mineral. In thin sections under the 
microscope, this rock was seen to be made up of waterworn frag- 
ments of shells, Foraminifera, Bryozoa, and corals, with a matrix 
of subcrystalline limestone. The rock very closely resembles, both 
macroscopically and microscopically, certain varieties of the Kentish 
Rag. 
The insoluble residue of this rock, which varied in amount in 
different samples from 3 to 18 per cent. of the whole, was found to 
consist of glauconite grains more or less decomposed, fine particles 
of sand, and some clayey matter. In this respect it also resembled 
Kentish Rag, a typical example of which yielded 104 per cent. of 
insoluble matter of a like kind. 
But as we proceed downwards, these limestones appear to gradually 
alter in their character and pass into a rock of a totally different 
appearance, when viewed in thin sections under the microscope. 
These lower beds of limestone are found to consist of a fine-grained 
calcareous paste, through which are scattered in greater or less 
. abundance oolitic grains, fragments of bivalves, small univalves, and 
Foraminifera coated with a film of calcic carbonate, the whole being 
impregnated with finely divided iron-pyrites. These limestones 
make up a bed about 9 ft. 6 in. thick, which is interrupted at 
a depth of 4 ft. from its upper surface by a band of clay about 9 
in. in thickness. The careful washing of this clay band yielded 
the following results. It contained an immense number of detached 
oolitic grains, a number of waterworn shells, Bryozoa, Foraminifera, 
and fragments of Echinoderms, often coated with a deposit of calcic 
carbonate. In lesser numbers are found grains of glauconite, par- 
ticles of iron-pyrites (often oval in form and with beautifully 
bright surfaces), fragments of teeth, and spines of fish, and very 
much worn and eroded fragments of Belemnites. In addition to 
these were many particles of imperfect coaly material, and a few 
of anthracite, also some waterworn fragments of sandstone and 
other hard rocks. 
A careful study of the substances contained in this clay band leads 
me to the conclusion that they are for the most part derived from 
the limestone strata which, as we shall presently see, underlie 
the curious series of deposits we are now describing. A few speci- 
mens of Foraminifera and Ostracoda appear to have belonged to” 
