126 
THE CRETACEOUS ROCKS OF BRITAIN. 
Coming next to the question of whether the zone of Ammonites 
Mantelli may be considered to represent the whole of the 
zone of Ammonites varians, we certainly think it more likely 
that it only represents a part. Taking the development of the 
latter zone in the Isle of Wight as a standard of comparison, we 
doubt whether the Devonshire zone of Am. Mantelli represents 
more than the lower 40 or 50 feet of it. We suspect that the plane 
of separation between the beds numbered 12 and 13 by Mr. Meyer is 
a hiatus equivalent in time to the formation of three parts of the 
Lower Chalk of the Isle of Wight and to most if not all of the Lower 
Chalk of Chard and West Dorset. There is, however, a possibility 
that Bed 13 may represent the subzone of Actinocamax plenus, and 
this will be discussed later on. 
In respect of thickness the zone of Ammonites Mantelli varies very 
greatly ; it is greatest at Wilmington, where it is probably over 
40 feet thick, and south of this, in Hooken Cliff, it is 24 feet thick, 
but thins away rapidly both to the east and to the west along the 
Coast, being often only two or three feet thick, and at one place 
(Charton cliff) it seems to be absent altogether. 
A complete list of the fossils which have been found in the zone 
of Am. Mantelli along the coast will be found in a separate column 
of the General List in Volume III. The fullness of this list is largely 
due to the labours of Mr. Meyer, who has visited the coast many 
times for the purpose of collecting from these beds. Collections were 
also made by myself and by Mr. Bhodes for the Geological Survey. 
The Wilmington Outlier. 
The occurrence of hard calcareous sandstone, locally known as 
“ grizzle,” was mentioned by Dr. Fitton in his well-known Memoir, 
and in the following terms :—“ In a large pit or quarry at the bottom 
