A HISTORY OF BEDFORDSHIRE 
sandy clay containing phosphatic nodules and numerous organic remains. 
It is regarded as the westerly extension of the Cambridge Greensand, 
the fossils which it yields being identical with those found in this bed 
in Cambridgeshire. The phosphatic nodules, with their associated 
fossils, have in all probability been derived from the denudation of the 
Upper Gault, which appears to have extended before this period con- 
siderably to the west of its present limit. The Chloritic Marl extends 
from Arlesey in the extreme east of the county, westerly by Shillington, 
Barton, and Sharpenhoe, and probably so far as Harlington, towards 
which place it is concealed by newer beds. 
During the period in which the coprolite-pits were being worked, 
numerous fossils were brought to light, especially in the neighbourhood 
of Barton and Sharpenhoe. That the assemblage of organisms was very 
remarkable may be seen from its inclusion of the reptilian genera Ich- 
thyosaurus, Plestosaurus, and Pterodactylus,and the cephalopods Ammonites 
auritus, A. studert, A. mantelli, and Belemnites minimus. Some of these 
were derived from the Gault during the extensive denudation to which 
it was subjected, and others are of the age of the bed in which they occur; 
but when the attempt is made to distinguish between the two series, the 
difficulties which present themselves are well nigh insuperable. An 
attempt to do so has however been made by Mr. A. J. Jukes-Browne in 
a paper ‘ On the Relations of the Cambridge Gault and Greensand.’’ 
The Cuatk Mart is an impure limestone, dark in hue and some- 
what plastic in texture, which features are due to a small admixture of 
silt. Its mineral composition indicates that it was deposited in much 
deeper water than the Gault. It attains its maximum development over 
an area which extends due east from Berks through the counties of 
Herts and Beds, north and south of which it rapidly diminishes in 
thickness. This change is accompanied by differences in its mineral 
constituents, that to the north indicating an increase in the depth of the 
sea in which it was laid down, and that to the south-west a decrease in 
the depth. 
During the progress of the works connected with the extension of 
the Midland Railway, numerous fossils were found in this stratum, some 
of which are worthy of mention. Two specimens of a previously un- 
described crustacean were obtained (one from the dark grey portion of 
the bed and the other from the higher and lighter-coloured part of it) 
which were figured and described, with specimens from elsewhere, by Dr. 
Henry Woodward under the name of Palega carteri.” The cephalopods 
include Ammonites varians in abundance, Actinocamax (Belemnites) lanceo- 
Jatus, a rare species, and Turrilites mantelli, previously recorded only from 
the south of England. Of reptilian remains a portion of a jaw of 
Ichthyosaurus campylodon with teeth im situ is the most noteworthy. 
The Chalk Marl, as well as some other divisions of the Chalk, 
contains numerous nodules of iron-pyrites, a mineral which is locally 
* Quart. Fourn. Geol. Soc. xxxi. 256-316. 
2 Geol. Mag. vii. 496, pl. xxii (1870). 
16° 
