Godwin- Austen— Cretaceous Rocks. 199 
here in much the same order of succession as there given; but not 
one has such a definite position in our Chalk as to justify the esta- 
blishment of stage-lines. It is unnecessary to extend this comparison 
to the remaining subdivisions of Dr. Reynes’ table—the lower Cre- 
taceous series, in the enormous development of the Lower Green- 
sand in the East and South-east of England, as compared with 
any part of continental Europe, shows that here were exceptional 
conditions. 
If in the South and West of France the Cretaceous series can be 
separated into definite ‘Etages,’ it can only be by means of the 
numerous forms of Rudistes which lived in those seas, and which 
were wanting in our more northern marine Province. These forms 
constitute the whole value of the minute systematic arrangements of 
the French Geologists. The remaining forms, taken by themselves, 
are insufficient for such a purpose. ‘The White Chalk of the South- 
east of England is a formation which represents conditions of con- 
tinuous accumulation, and of remarkable uniformity, through a 
vertical thickness of beds of more than a thousand feet. In this the 
remains of animal life are exceedingly scarce, relatively to the 
mass; and such as occur have a considerable range. So likewise 
with respect to the Chalk of the North of France. 
Dr. Reynés characterizes his uppermost horizon by Belemnitella 
mucronata and Bb. quadrata ; and to this he assigns our ‘Upper 
Chalk.’ The ‘Upper Chalk’ of England is a very vague term: it is 
merely that portion which happens to be uppermost; there is no 
part which has not been greatly denuded. The fossils of the flints 
of the gravel-beds show that they have been derived from the zone 
of Belem. mucronata and Micrast. cor-anguinum. The evidence as 
to the character of the Upper Cretaceous marine fauna is not to be 
met with either in the North of France or in England; but it may 
be found in Belgium and the Netherlands. The deposits are of 
great variety and thickness; they contain a copious fauna, amount- 
ing to nearly 1,000 species, of which only about 85 occur in our 
‘Upper,’ ‘ Middle,’ and ‘Lower Chalk,’ and in our ‘ Upper Green- 
sand.’ By the aid of the ampler evidence of this copious marine 
fauna, the Dutch and Belgian Geologists make an upper zone with 
Belem. mucronata, and a lower zone with Belem. quadrata; and 
each of them has a greater number of characteristic species, or 
species peculiar to it, than occur in the whole of the White Chalk 
series of this country taken throughout. The Cretaceous deposits, 
where such a subdivision is both obvious and necessary, as for 
Belgium, are geographically continuous with the Chalk of England 
and the North of France; and this suggests the second question 
raised by Dr. Reynes’ Memoirs: What in Geology is ‘an Horizon’— 
‘une Etage’? What is the evidence of synchronism? Of this I 
will attempt an answer in another communication. 
