﻿Yol. 64.] SUBDIVISIONS OP THE CHALK OF TRIMINGHAM. 401 



.23. On the Subdivisions of the Chalk of Trimingham (Noefolk).^ 



By Reginald Mare Betdone, P.G.S. (Read January 22nd, 



1908.) 



[Plates XLVII & XLVIII— Maps.] 



The Chalk in question is seen on the sea-shore when freed from 

 shingle and sands by favourable tides, and portions of it rise as 

 bluffs in the more recent deposits of the cliffs, being exposed from 

 time to time as these beds in their turn are denuded away. This 

 Chalk, by the evidence of its fossil contents, is younger than the 

 Chalk of the mucronata-zone, which is the highest member of the 

 White Chalk exposed elsewhere in England. This mucronata-Chalk 

 dips generally eastwards, and, although exposed between Weybourne 

 and Cromer, disappears just east of the latter place and is seen no 

 more. The Chalk described in this paper lies on the top of mucro- 

 naia-Chalk, and is correlated by its fossil-contents with the Chalk 

 of Riigen. It is, therefore, in normal succession to the mucronata- 

 Chalk, and represents the highest beds of the Cretaceous System 

 existing in this country. It has not been found in any other part 

 of the British Islands. 



The literature on it is scanty, and for present purposes it will 

 be useful to call attention to Mr. Clement Eeid's ' Geology of the 

 Country around Cromer' Mem. Geol. Surv. 1882; to the present 

 writer's ' Stratigraphy & Fauna of the Trimingham Chalk,' 8vo, 

 London (Dulau) 1900, and Geol. Mag. 1906, which gives a complete 

 fauna of these beds and of the mztcronaia-Chalk between Weybourne 

 and Cromer ; also to Mr. A. J. Jukes-Browne's ' Upper Chalk of 

 England,' vol. iii of the 'Cretaceous Rocks of Britain' Mem. Geol. 

 Surv. 1904. 



In a paper on the Chalk of Trimingham as a whole, published in the 

 Geological Magazine for 1906, I indicated that several subdivisions 

 of that Chalk could be made on lithological and palaeontological 

 grounds. The object of the present communication is to lay before 

 the Society a sketch-map showing the geographical distribution of 

 these subdivisions, with a brief account of their distinguishing 

 features. 



The main outlines of the map and nearly all the details have been 

 laid down from observations made with a finely-divided compass and 

 a tape-measure during the last thirteen months. For these practically 

 absolute accuracy may be claimed. But, in many instances, details, 

 and along the half-tide level on each of the three large blocks the 

 main outlines, could only be supplied from observations made during 

 the previous five years with a small compass and the distances paced. 

 But the possible error in the position of any point, or in the course 

 of the various lines of flints, can hardly ever be more than 10 feet 

 in any direction. Even now it will be seen that there are a few 

 areas where nothing is laid down positively, though Chalk must 



^ Edited for the Geological Society by C. Davies Sherborn, F.G.S., at the 



request of the Council and by consent of the Author. 



2d2 



