Godwin-Austen— Cretaceous Rocks. 197 
II. On THE CLASSIFICATION OF THE CRETACEOUS BEDS. 
By Ropert A. C. Gopwin-Austen, F.R.S., F.G.S. 
| ae two Memoirs by Dr. Reynés, on the Cretaceous formation, 
which were noticed in the ninth number of the GroLocicaL 
MaGazinr, suggest two questions: how far the subdivisions there 
proposed are applicable to the Cretaceous series of this country; and, 
next, as to the sufficiency of the ground on which the synchronism 
of the subdivisions of geological formations has been based. The 
subject of the second Memoir, ‘ De l’Etage,’ involves considerations 
which might be well extended to the whole range of the geological 
series : indeed, it will hardly be profitable to make much progress 
with the past physical history of the earth until rules for deter- 
mining geological horizons shall be established. 
The first of these questions has probably been answered much in 
the same manner by many English Geologists. Things do not admit 
of subdivision and the comparison of relative parts, unless they have 
something in common. Dr. Reynés proposes ten subdivisions for the 
Cretaceous series, each characterized by from three to four forms of 
Shells or Urchins. Out of thirty-eight species which are cited, as 
many as eighteen have not hitherto been recognized within the 
British area; so that twenty species alone serve for comparison, 
or an average of two for each ‘stage.’ This is a small amount of 
evidence. In that school of Paleontology, however, in which it is 
a fundamental doctrine that a species has a definite duration in 
time, and that identical forms, wherever met with, are proofs of 
synchronism, a single species would have done as well. 
The twenty species which have to be removed from Dr. Reynés’ 
list belong to the Mediterranean province of tlre Cretaceous Period, 
with which he is best acquainted. 
Dr. Reynés’ highest horizon* is that with Belemnitella mucronata, 
B. quadrata, Micraster cor-anguinum, and Hemipneustes radiatus : 
this last, a well-known form from the Maestricht and Gulpen beds, 
has not been found in England. The three other species may be 
placed thus :—Belem. mucronata, Micraster cor-anguinum, and 
Belem. quadrata. 
These forms, which are abundant in the Chalk of the North of 
France, of Belgium, and of England, do not occur in the Cretaceous 
beds of the Mediterranean area; and on such grounds the uppermost 
division of the series might be supposed to be wanting there. Nor, 
if recourse be had to considerations which will be noticed in the 
sequel, can there be any comparison established between the Upper 
Chalk of England and that of Maestricht. 
In the horizon next below the second, the forms cited are Radio- 
lites, Spherulites, and Hippurites, with Micraster brevis and Ostrea 
auricularis. M. brevis may be only a Mediterranean-area variety of 
M. cor-anguinum ; but the form does not occur with us, nor in the 
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* Upper Chalk—Chalk of Maestricht and Meudon. 
