128 A. J. jrKES-BEOWXE OX THE 



places divided from it by fhe beds marked h (sands and gravel)"*. 

 He adds that though sometimes it is difE.cult to say where one clay 

 ends and the other begins, in other places the division is very 

 distinct, 



IS ow the facts I have adduced appear to me sufficient of themselves 

 to invalidate Mr. S. Wood's classification, and, as a necessary 

 consequence, to destroy the superstructure of theory Tvhich he has 

 built upon it. Mr. Wood hardly seems to recognize the difference 

 between widespread unconformity and local contemporaneous erosion. 

 If the succession were broken in the manner assumed by ^Ir. TTood, 

 and if the interval between the formation of the Purple Clay and 

 the Hessle gravel were of such length and importance that it could 

 be taken as the line of division between the Glacial and Post-glacial 

 periods, then this break must be a widespread one, and must be 

 universal throughout the east Yorkshire and Lincolnshire area. 



But if, on the contrary, it can be proved that at two or three 

 localities there is a complete passage from one clay into the other, 

 then it is clear that the break is not a universal one, and the line 

 of division becomes one of comparative insig-nificance. 



In the face of such sections as those at Cleethorpes, Louth, and 

 Ludborough, where no break exists, it is useless to multiply instances 

 where the clays are separated by beds of gravel and sand, and where 

 some local erosion appears to have taken place. Still more unrea- 

 sonable is it to argue from these local appearances, and from the 

 occurrence of Cyrena jiuminalis in the gravels, that the Hessle beds 

 should not be regarded as Glacial, but as Post-glacial deposits. 



I can see no valid reason why the whole series of Boulder-clays 

 and gravels in east Yorkshire and Lincolnshire should not be 

 classified as Glacial ; and I look upon those above the basement 

 clay as forming one continuous series, so far as any series of Glacial 

 deposits can be called continuous. That cases of local erosion by 

 currents should occur, and that beds of gravel and sand should be 

 intercalated between the Boulder-clays, are natural incidents in a 

 series of deposits which have been formed near coast-lines by the 

 agency of marine ice; and my conviction that these Boulder-clays 

 have been so formed has only been deepened by my recent 

 experiences and observations. 



§ 5. Conclusions. 



In section 3, we came to the conclusion that the brown and 

 mottled clays of the Pen-border and the Ancholme valley were 

 newer than the Chalky Boulder-clay of those districts ; further that 

 there was a decided break and an apparent unconformity between 

 the two groups. In the last section I denied the existence of any 

 break in the Brown-clay series of East Lincolnshire (i.e. the Purple 

 and Hessle Clays), and showed that Mr. Lamplugh holds the same 

 opinion with regard to the continuity of this group along the 

 Holderness coast. It seems therefore only reasonable to conclude in 

 the first place that the Glacial beds found on the west and on the 

 * Quart. Jouni. Geol. Soc. vol. xxiv. p. 147. 



