98 
THE CRETACEOUS ROCKS OF BRITAIN. 
It will be noticed that this total of 107 feet only exceeds the thick, 
ness at Worbarrow Bay by just the thickness of the sandy base¬ 
ment bed. 
Of the section in Lulworth Cove, Mr. Strahan says that it is 
less accessible than that of Mupe Bay, “ but the marl-bed can be 
reached without difficulty on the north-west side of the cove.” 
Mr. Strahan evidently assumes, as previous observers have done, 
that this band of marl, which is about six feet thick, is the Belem- 
nite Marl, but he does not attempt to explain its position, which 
is little more than 30 feet above the basement-bed. Professor 
Barrois measured the section in 1875,* and made the thickness of 
beds between the base of the Chalk to the base of the marl-band 
from 32 to 35 feet. Mr. W. Hill measured the same space in 
1892,f and made it from 30 to 32 feet; but on his last visit in 
1901 he noticed that the true Belemnite marls were either cut 
out by a slip fault or were hidden by talus. 
The marl-bed which has hitherto been taken for the subzone 
of Actinocamax plenus is of a yellowish-grey or buff colour, 
and weathers into thin platy pieces, thus having a different 
aspect from the bluish-grey Belemnite Marl of Mupe Bay. Mr. 
Hill therefore came to the conclusion that it was not the 
Belemnite Marl, but a development of one of the layers of marl 
which occur throughout the zone of Iiolaster subglobosus in Mupe 
Bav. The real Actinocamax marl is not seen in the cliff, but 
Mr. Hill noticed a fallen block on the shore, which consisted of 
marl having the usual local character of that band; and it was 
probably from such a block that Professor Barrois obtained the 
specimen of Act. plenus which he records as found here. Only a 
small area is accessible, and neither Mr. Hill nor Mr. Rhodes 
succeeded in getting fossils except from the basement-bed, but 
the total thickness of the Lower Chalk is probably from 75 to 
78 feet. The following are the details of this section as measured 
by Mr. Hill: — 
ft. 
White chalk in lenticular beds, with partings of greenish 
marl - -- --.20 
Smooth grey marls --------6 
White chalk divided into beds by thin seams of marl - 16 
Blocky white chalk with siliceous concretions - - - 12 
Glauconitic chalk with phosphatic nodules and some fossils 4 
58 
In Hurdle Cove the chalk is too much crushed and faulted to 
be measurable (see p>. 419). 
At White Nothe the cliff above the Chert Beds shows, according 
to Mr. Strahan, from 40 to 45 feet of chalk, smooth and white, 
with some layers of marl, and having three layers of flinty nodules 
* Recherehes sur le Terrain Crc't. Sup. 1876, p. 93. 
t Quart. Journ. Geol. Soc. Vol. lii. p. 109. , __ f 
