MIDDLE CHALK—CAMBRIDGESHIRE. 
469 
fault. This flexure is exposed in a series of quarries ; it appears 
to commence near Tlierfield, crosses the North Road (Ermine 
Street) about two miles south of Royston, and curves round by 
Newsells Bury, Smyth's End (Barley), Great Chishall and Heydon, 
At all these places the beds are bent into an anticline, the northern 
limb of which plunges down the slope of the escarpment. 
Whether they are cut oil’ by a fault or whether the curvature is 
continued by a corresponding svncline we do not know, but there 
must be either a fault oi* a syncline along the lower slopes of the 
escarpment, as the chalk near Royston has normal southerly dips. 
If there is no fault, there would be a second outcrop of the Chalk 
Rock to the north of this series of exposures, but no such outcrop 
was found. 
Stratxgraphidal Details . 
Zone of Rhynchonella Cuvieri.— The outcrop of the 
Melbourn Rock enters Cambridgeshire near Ashwell Station, on 
the Hitchin and Cambridge Railway. 
The upper part of this zone, with some of the overlying zone, is 
exposed in the large quarry in Morden Plantations. The upper 
level of this quarry shows : — feet. 
Soil and chalk rubble -------- 4 
Bedded white chalk with a few flints ----- 20 
Tough yellowish rocky chalk ------- 1 
Rather soft white chalk, with scattered flints and a course of 
elongate finger-like flints 10 feet down. This chalk 
contains Galerites subrotundu.% Gal. castanea, Rhyn¬ 
chonella Cuvieri , Terehratula semiglobosa and teeth of 
Ptychodus --------- 12 
The lower level shows :— 
Chalk between two layers of Hints ----- 3 
Tough yellowish chalk full of Inoceramus myiiloides , dipping 
eastward - -.-15 
The yellowish band in the upper level may perhaps be taken 
as the upper limit of the Rh. Cuvieri zone. 
The base of the zone is exposed in a pit by the side of Ermine 
Street, more than a mile north of Royston, and the section as taken 
in 1885 was as follows : — f ee t. 
Soil and hard bedded chalk - - - - - - 6 
MnlLrvnrn f Hard yellowish chalk with thin marly partings con- 
p y > taining nodules - - - - - - 31 
occ ‘ Hard nodular whitish chalk ----- gj 
/Lenticular beds of marly chalk - - - - - 2 ~ 
Lower j Hard marbled chalk, grey and white - - - - 1 
Chalk. | Grey marly chalk - - - • - - - 1 
l White chalk ------ geen f or 3 
The Melbourn Rock is also well exposed in the lime-kiln quarry 
south of Melbourn, thus : — f ee t. 
Soil and broken chalk. q 
Bedded whitish chalk - -- -- -- -4 
if n p i /Hard yellowish bedded chalk - - - - 4 
1 ‘ K ‘\Hard rough nodular chalk, massive - - 31 
Lower Chalk, marls, etc. (see p. 199) ----- 30 .J 
4219. h H 2 
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