BOULDER-CLAYS OF LINCOLNSHIRE. 131 



marine shells in Xorth Lincolnshire to levels of about 200 feet may 

 be evidence of this depression. During this submergence the glacial 

 conditions seem to have passed awa}^, and the land was gradually 

 and finally reelevated. 



We may, with Mr. Searles Wood, call the two epochs when thick 

 masses of Boulder-clay were formed, the periods of major and minor 

 glaciation ; but the latter would for me include the formation of the 

 Purple Clay. It is, indeed, this point which I wish to bring out in 

 a strong light: the paragraphs I have just written are purely theo- 

 retical and may not really represent anything like the actual 

 sequence of events ; but my statement of the close connection between 

 the Purple and Hessle Clays rests upon personal observation and 

 not upon theoretical grounds. What, therefore, I chiefly insist upon 

 is this, that if there is any one great break in the Glacial series, 

 corresponding to a decided change in physical conditions, this break 

 is not at the base of the Hessle beds, where Mr. Searles Wood puts 

 it, but at the base of the Purple Claj- in the Holderness section. 



I do not propose to do away with the terms Hessle and Purple 

 Clay, because they may be useful as indicating certain horizons in 

 the Brown-clay group. I only wish to correct what appears to me 

 an error in the accepted classification of the Glacial series, and to 

 degrade the Hessle Clay from a position of primary importance to 

 one of secondary or perhaps even of third-rate rank. 



I would simply tabulate the Glacial series as below : — 



Newer Glacial 



Lincolnshire. Yorkshire. 



{Hessle Clay. Hessle Clay. 



Purple Clay. Purple Clay. 



r Chalky Clay. Basement Clay. 



Older Glacial . . . . ^ Cromer Series (includ- 

 [ ing Middle Sands). 



Discussion. 



Mr. UssHER expressed his agreement with the views of the author, 

 so far as the Brigg section is concerned. He had been greatly 

 indebted to the author in arriving at correct ideas on the relation of 

 the Boulder-clays while mapping that district. 



Mr. C. Reid had surveyed part of North Lincolnshire and Holder- 

 ness. He thought that the Hessle Clay, at Hessle, is only a weathered 

 and decalcified Boulder-clay, and it was unsafe to correlate it with 

 the beds at Kelsey Hill or on the coast. He insisted that the 

 different colours of the Boulder-clays and the absence of chalk from 

 them were frequently due to weathering. 



Mr. De Range asked the last speaker if the shells in the Boulder- 

 clays were similar in type to those found in the intercalated sands. 

 He wished to know if there were any real evidence of intercalation 

 of a fauna characteristic of a milder climate than that indicated by 

 the shells of the Boulder-clay. 



