331 
THE CRETACEOUS ROCKS OF BRITAIN. 
CHAPTER XXVIH. 
THE MIDDLE CHALK IN SURREY. 
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General Description. 
The Middle Chalk of Surrey is similar to that of West Kent. It 
has a well-marked band of Melbourn Rock at the base with a thick¬ 
ness of 12 to 14 feet. This is succeeded by the firm and rather 
rough chalk which forms the rest of the Rhynchonella Cuvieri zone, 
and this by the softer and whiter chalk of the Terebratulina zone. 
Above this the chalk becomes irregular and lumpy, a character 
which, as in Kent, is associated with a great increase in the number 
of flints, and with the occurrence of the fossil Holaster 'planus. 
The total thickness of the Middle Chalk along the outcrop in 
Surrey is probably over 200 feet, but there is no continuous section 
through it, and the high dips make it difficult to estimate its 
thickness. 
The deep borings in the London basin do not afford very satis¬ 
factory accounts of the Middle Chalk, for the particulars given 
are chiefly from the notes of foremen well-sinkers, and few speci¬ 
mens have been examined by geologists. At Streatham the thick¬ 
ness of the Middle Chaik is given by Mr. Whitaker* as 219 feet, but 
from Mr. Hill’s notes of the specimens printed in the same memoir 
I gather that the Melbourn Rock is probably represented by the 
10 J feet between the depths of 682 and 692J feet, while the bi.se 
of the Hoi. planus zone may be a few feet below the depth of 463 
feet; hence the thickness of Middle Chalk indicated by the Streat¬ 
ham boring is probably from 222 to 225 feet. 
At Richmond the division appears to be much thinner, the lower 
zones, including the Melbourn Rock, being only about 150 feet 
thick, surmounted by a hard nodular rock of the western Chalk 
Rock type. 
In the boring at Winkfield, near Windsor, the thickness of this 
part of the chalk appears to be 169 feet, including 14 feet of Mel¬ 
bourn Rock. 
Stratigraphical Details. 
► 
The following account of exposures in Surrey is based on notes 
taken by Mr. W. Hill during a traverse made in 1897, to which 
are added quotations from those of previous observers. 
Zone of Rhynchonella Cuvieri. 
Melbourn Rock is exposed in the cutting at the north entrance 
of the tunnel between Warlingham and Oxted ; a view of this is given 
* Geology of London, Vol. ii. p. 225 (1889). 
