186 
THE CRETACEOUS ROCKS OF BRITAIN. 
The “ Coprolite-bed,” or Cambridge Greensand, sets in near 
Harlington, and was worked in 1874 between the villages of Sharpen- 
hoe and Barton. The following account of the section exposed in 
a working near Sharpenhoe is quoted from my paper on the “ Bela- 
tions of the Gault and Cambridge Greensand.”* 
The beds then seen were as follow : — 
/ Greyish-white marl - - 
Greenish-grey marl, with a few buff-coloured phos- 
Ohalk; / phatic nodules - ------ 
Marl. | Bluish argillaceous marl- - 
! Bluish-grey sandy clay, with green grains, many 
nodules and fossils ------ 
Gault—Blue Clay below. 
4 
2 
1 
The nodule-bed is “ the representative of the Cambridge Green¬ 
sand, but its appearance is very different. There is less sand and 
glauconite, and most of the coprolites are formed of a lighter 
coloured phosphate, though some are of the usual black colour; 
These latter, however, have not been subjected to the same amount 
of rolling as those in Cambridgeshire, the small Ostrece and Plicatulw 
upon them being in much better preservation, and fine striations 
being visible on the latter which I have never seen before.” 
The inference from these facts was that these phosphate nodules 
had not travelled so far, but were nearer their original source than 
those of Cambridgeshire; this source being the Upper Gault marls 
which still exist in Buckinghamshire and extend a short distance 
into Bedfordshire, but are cut out by erosion toward the north¬ 
east, though they may extend below the Chalk to the eastward 
between Hitchin and Ware. 
Coprolites were also largely dug by Higham Gobion and Shilling- 
ton between the years 1868 and 1875, and again at Arlesey, north of 
Hitchin, where the following notes were taken by Mr. Whitaker 
at the Arlesey Cement Works in 1868: — 
The Chalk Marl, 8 to 12 feet, passes down into marly clay with green 
grains and dark nodules. At one part the green grains occur up to 4 
feet above the Gault, but in the weathered part of the section the 
junction bed appears as a pale green layer of 2j feet, the nodules being 
chiefly in the bottom part, a layer resting on the Gault. The Gault is 
exposed for 10 or 12 feet, and the junction is well marked, with a very 
slight southerly dip. 
Writing of the pits which were opened near Asliwell and Morden 
between 1866 and 1874, Mr. H. G. Fordham saysf—“ The bed [i.e. 
Cambridge Greensand]. is from 18 inches to 3^ feet in thickness, 
and varies considerably in the proportion of nodules. It graduates 
into the Chalk Marl above, the glauconite grains extending higher 
than the nodules, and the nodules being more abundant in the 
lower part of the bed.” 
■5f 
Quart. Journ. Geol. Soc., 1875, Vol. xxxi. p. 202. 
Proc. Geol. Assoc., Vol. iv. (1878), p. 150. 
