190 
THE CRETACEOUS ROCKS OF BRITAIN. 
The top of the zone is again seen in a quarry three-quarters of 
a mile S.S.E. of Litlington Church. The section is given on p. 199, 
and it is noteworthy that about 6 feet from the top there is a layer 
of hard gritty chalk with green grains and green-coated nodules, 
very like the bed at Sundon, and certainly at a higher horizon 
than the Ivinghoe Rag, for there are no signs of erosion here. 
Belemnite Beds. —These beds are exposed in many of the 
quarries and sections where the Melbourn Rock is seen; as, for 
instance, in the quarry by the railway south-east of Leagrave, 
near Luton, which shows : — 
ft. 
Melbourn Rock. ---8 
{ Yellowish-grey shale, with a few nochiles of hard 
chalk - 
Hard compact white chalk ----- 2 
Thin layer of grey shale (2 inches) - — 
Blocky whitish chalk, streaked with grey in the upper two 
feet - -- -- -- -- seen for 22 
The central bed of white chalk is here unusally thick, and the 
lower marl thinner than usual. 
One of the best sections of the upper part of the Lower Chalk, 
including the Belemnite band and the base of the Melbourn Rock, 
is exposed in the large quarry by Grove Mill, one mile south-east 
of Hit-chin! This has been cut back considerably since the writer 
saw it, and he is indebted to Mr. W. Hill for the following account 
of the section now visible : — 
Soil and rubble - - - 
Hard rough white chalk (base of Melbourn Rock) - 
^Irregular bed of buff-coloured laminated marl, 
with lenticular courses of hard whitish chalk 
j Hard smooth white chalk - 
IGrey laminated marl - - - - - 
Smooth blocky greyish-white chalk - 
Thin marly layer ------ 
Thick-bedded whitish chalk - - - - 
.Pale grey chalk, in thick beds - - - - 
Belemnite I 
Beds. 
Zone of 
II. sub-, 
globosus. 
ft. in. 
1 0 
2 0 
1 3 
1 10 
0 4 
1 6 
0 3 
25 0 
15 0 
At the spot where these measurements were taken the lower 
marl-bed is very thin, but a few yards to the eastward it thickens 
and becomes a well-marked bed. About 20 feet below this marl 
there is a band of brown-stained chalk, which extends for some 
distance, but dies out to the southward. Above it is a thin seam 
of brownish clay washed in from the surface. 
Another good section is in a quarry west of Willbury Hill, near 
Hitchin, where the lower marl has its ordinary thickness of 10 or 12 
inches, and the zone as a whole is 3 J feet thick. It was also exposed 
when the cutting on the Great Northern Railway at Cadwell was 
being widened in 1885, and here the compact white chalk is replaced 
by “ marbled chalk,” greyish with included lumps of white : fossils 
are very abundant in this bed, especially Terebratulce , Rhynchonella 
plicatilis, Ostrea vesicularis, and Actinocamax plenus , but are almost 
all broken. The upper marl is also thicker and more calcareous 
than usual, the three beds having a united thickness of feet. 
