114 A. J. JTJXES-BEOWITE OF THE 



16. T7ie Botjldee-Clats of LnfcoxT^sHiEE. Their Geogeaphical 

 EAifGE and Eelatiye Age. By A. J. Jukes-Bkowne, Esq., 

 B.A., F.G.S. (Bead January 28, 1885.) 



(Communicated by permission of the Director-General of the Geological 

 Survey.) 



Jntrodtiction. 



When I commenced the snryey of East lincolnsliire, in 1877, the 

 only connected account of the Boulder-elay was to be found in the 

 well-known paper by Messrs "Wood and Bome * ; and up to 1879, 

 when I wrote a paper " On the Southerly Extension of the Hessle 

 Boulder-clay in Lincolnshire " f, I saw no reason for doubting the 

 propriety of their classification. 



The mapping of these clays by myself and colleagues during the 

 subsequent progress of the Surrey has, however, brought to light 

 many facts ^I'hich were unknown to Mr. Searles Wood, and has led 

 us to question the accuracy of his interpretation of those facts which 

 were known to him. 



The classification of glacial deposits is always a difficult matter, 

 and in Lincolnshire there are special circumstances which make it 

 very difficult to ascertain the relative age of the several masses of 

 Boulder- clay. 



Mr. Searles Wood himseK, though still adhering to the divisions 

 which he first established, has considerably modified his views with 

 regard to the correlation of the Lincolnshire Boulder- clays. His 

 original classification of the glacial scries in East Yorkshire and 

 Lincolnshire, as published in 1868 t, was as follows : — 



5. Hessle clay. 



4. Hessle sand and gravel. 



3. Purple clay. 



2. Sands and gravels. 



1. Basement clay. 



He then regarded the Basement clay as the equivalent of the 

 East Anglian Upper Boulder-clay, and considered the overlying 

 Purple and Hessle Clays as newer than any part of this southern 

 Chalky Boulder-clay. In his last paper (1880) he takes a difierent 

 view, and appears to look upon the Basement and Purple Clays as 

 together representing the whole East Anglian series §. 



In both memoirs he insists upon the existence of a great break at 

 the base of the Hessle beds, and even goes so far as to exclude these 

 beds from the glacial series altogether, grouping them as Post- 

 glacial, because they are bedded into the Wold valleys and because 

 at one locality they happen to contain the shell Cyrena fiumindlis, 



* Quart. Joum. Geol. Soc. vol. xxiv. p. 146. t Op. cit. vol. xxxv. p. 397. 



^ Loc. cit. 



§ Quart. Journ. Geol. Soc. vol. xxxvi. p. 527. 



