374 
THE CRETACEOUS ROCKS OF BRITAIN. 
Dover cliffs for the purpose of revising his previous description 
and of fixing on the most convenient plane for the summit of 
this division. 
Still more recently the two zones comprised in the Middle 
Chalk have been described by Dr. A. Rowe. * 
The following account of the beds seen in these cliffs has been 
drawn up from Mr. Hill’s paper and from his subsequent notes. 
The lower beds are most accessible by the cliff path at the western 
entrance of the tunnel through Shakespeare’s Clift* (see Fig. 24, 
p. 35), and though the very highest part of the Middle Chalk 
occurs in this cliff, it is inaccessible, and the higher beds must be 
studied on the shore east of Dover (see Fig. 67). 
Zone of Rhynchonella Cuvieri. 
The lower part of this is the “ Grit-bed ” of Price, and is 
undoubtedly the equivalent of the Melbourn Rock, although it here 
attains a much greater thickness than in any other locality. The 
lower 12 feet consists of hard whitish nodular chalk streaked with 
veins of greyish marly material, while the upper 20 feet is yellowish 
and less compact, the nodular layers weathering out very con¬ 
spicuously. In these respects it closely resembles the Melbourn 
Rock of the Midlands. Discoidea minima and Cardiaster yygmceus 
are the two commonest fossils, but Galerites subrotundus appears 
at the top of the bed. 
Above the “ grit-bed ” there is rather hard yellowish chalk con¬ 
taining harder nodules, which are arranged in more or less definite 
layers, which, however, become more distant, and the chalk between 
becomes gradually softer in the higher part of the zone. 
This nodular chalk extends for about 38 feet, giving by our 
measurements a total of 70 feet to the zone of Rhynchonella Cuvieri. 
This is rather less than the thickness assigned to the nodular chalk 
by Professor Hebert (his zone of Ammonites nodosoides ), which 
was 82 feet, but it closely corresponds with the measurement of 
Mr. F. Drew, who found the “ concretionary chalk ” to be 73 feet 
thick.f Rhynchonella Cuvieri and Inoceramus mytiloides (= labiatus) 
are the prevalent fossils in this part of the zone. 
The Terebratulina Zone. 
This zone consists of dull white rather soft friable chalk, with 
many thin seams of greyish marl, and in the upper part it contains 
several layers of flint nodules, each at some distance from the other, 
except the two highest layers, which are near together. The total 
thickness is about 160 feet. 
Above the highest well marked nodular layer, which is taken 
as the top of the underlving zone, the small Brachiopod Terebratw- 
lina gracilis var. lata , occurs abundantly both in Shakespeare’s 
* Proc. Geol, Assoc., Vol. xvi., p. 315 (1900), 
+ In Whitaker's Geology of the Loudon Basin, Mem. Geol. Snrvev, 1872, 
Vol. ix., p. 3 . * ' 
