A. J. Jukes-Browne—The Subdivisions of the Chalk. 257 
rock-beds which are so conspicuous in Cambridgeshire. I have 
already indicated where the Melbourn Rock may possibly be found; 
but whether the Chalk Rock is continued northward, with the same 
characters that it exhibits near Royston and Saffron Walden, is 
perhaps more doubtful. Still it is quite possible that certain 
yellowish nodular layers will be found at .the top of the Holaster 
planus zone, as is the case near Newmarket, and that these may be 
taken as the line of division between the Middle and Upper Chalk. 
There is, indeed, every reason to expect that the higher zones of the 
formation will eventually be satisfactorily correlated throughout 
England, France, and Belgium, since the conditions under which 
they were deposited were certainly more uniform than those which 
prevailed during the earlier part of the Cretaceous period. 
In conclusion J would remind you that the credit of first proposing 
the tripartite division of the Chalk belongs to the Norfolk 
geologist—Samuel Woodward. He marked out the broad outlines 
of what I have little hesitation in calling the true and natural 
classification, and drew up separate lists of the fossils found 
in each division. It is astonishing that English geologists should 
not have pursued the study of the formation on the lines suggested 
by these early writers, especially as a similar system was being 
adopted and developed in France; so that it has actually remained 
for French geologists to demonstrate the applicability of this system 
to the Chalk of our own country. Much however still remains to be 
done in completing our knowledge of faunas of the different zones, 
and every one who makes a collection of fossils from any part of the 
Chalk, and is careful to record the exact zone and quarry where each 
specimen was obtained, will be rendering valuable assistance. 
CLASSIFICATION OF THE CHALK. 
YU SIPPIAL WeGd “A 
APU 1A MOT 
S. Woodward, W. Whitaker, 1865. Caleb Evans, 1870-77.|  Jukes-Browne, 1880. 
1833. Norfolk. Bedford and Bucks. Kent and Surrey. Cambridgeshire. 
Upper Chalk. White Chalk with flints. | Riddlesdown Beds| Zone of Micraster 
cor-bovis. 
Chalk Rock. Chalk Rock. ! 
Zone of Holaster ) 
White chalk with thin | / Kenley Beds. planus. | 
Medial Chalk layers of grey marl, and | } Whiteleaf Beds | Zone of Teredratu- | 
with few flints. a few flints in upper | ) Upper Marden lina gracilis. > 
part. . Park Beds. Zone of Rhyncho- | 
nella Cuvieri. | 
Melbourn Rock. ‘J 
{| Hard bedded chalk with | Lower Marden Zone of Holaster ) 
| thin marly layers. Park Beds. subglobosus. 
Lower Chalk y Blocky chalk with curved Totternhoe Stone. | 
without flints. }| and irregular bedding. f ‘ Zone of Rhyncho- 
| | Totternhoe Stone. Sil ios dee | nella Martini = 
| Totternhoe Marl. (| Chalk Marl. | 
Chalk Marl. | Chloritie Marl ?. Cambridge Green- | 
sand. J 
Red Chalk. 
DECADE II.—VOL. VII.—NO. VI. 17 
