﻿410 ME. E. M. BEYDOXE OX THE [-^l^e* IQO^i 



to the Xorth Bluff is about 40 yards, it is clear that the face of 

 LyelFs bluff was farther seaward than the point at which the neck 

 starts, that is to say at least, and possibly much more than^ 40 yards 

 seawards of the present high-water level. As his figure of the 

 Bluff indicates that it was at least 25 feet high, we have a mass of 

 Chalk of the same superficial area as the neck leading to the ^orth 

 Bluff and 25 feet in depth removed in about 70 years ; so that 

 there is hardly any limit to be set to the amount of Chalk which 

 may have existed above present levels to seawards in Glacial times 

 and have since been destroyed. If, as is likely, the Bluffs in 

 Lyeirs day stood about equally distant from high-water level, the 

 above calculation makes it fairly probable that the southernmost 

 bluff of Lyell's day — which disappeared long ago — stood along the 

 landward edge of some part of the block (B) above described, and 

 not on any part of the ridge with the pseudotabular flint, which 

 otherwise would seem the natural position to assign to it. 



There is one more point to be considered, that is, the name to be 

 attached to the zone created for the Trimingham Chalk if, as 

 appears to be the case, it is inevitable that a zone should be created. 

 Mr. Jukes-Browne ^ has suggested that the zone should be called 

 ' zone of Ostrea lunata/ as characterized by the association of 

 Ostrea lunata, Pecten serratus, Ecliinoconus abhreviatus, Trocliosmilia 

 comucopice, Thecidium vermiculare, Terehratulina Gisei, and 

 T. gracilis. Jfow, Pecten serratus, Ecliinoconus abhreviatus, and 

 Trocliosmilia cornucopice are all well-known and abundant fossils in 

 the zone of Belemnitella raucronata in Norfolk, and are therefore 

 of no use in separating the Trimingham Chalk from the zone of 

 B. mucronata. I have shown that Ostrea lunata does not occur at 

 all in more than half of the total thickness of Chalk exposed ; 

 wliile Thecidium vermiculare only occurs freely at one or two 

 horizons in the O.-lunata Chalk, is very rare indeed in any White 

 Chalk without 0. lunata, and probably does not occur at all in 

 any Grey Chalk. I have, therefore, objected to the adoption of 

 Mr. Jukes-Browne's zone, because it is by its very definition inap- 

 plicable to the greater part of the Chalk which it is intended to 

 cover, and such an objection would appear to be necessarily fatal. 

 Hence the zone of Chalk at Trimingham. lying above the zone of 

 Belemnitella mucronata, now divided and defined by me for the first 

 time, requires a name. 



The net result of this paper is to make it possible, for the first 

 time, to form some idea of the extent and nature of the Chalk of 

 Trimingham, which has been practically ignored by everyone who 

 has discussed the Bluffs, except Mr. Clement Reid and Mr. Jukes- 

 Browne. 



I still adhere without reservation to the view expounded in the 

 Geological Magazine (1906, pp. 124, 125), that these enormous 

 masses of Challv can only be in situ and must have once formed 

 part of a large continuous mass ; and that, as the various existing 



^ ' The Upper Chalk of England.' toI. iii of the ' Cretaceous Koeks of Britain' 

 Mem. Geol. Sury. V. K. (1904) p. 12. 



