510 J. Lam/plugh — Marine Shells in Boulder-clay. 



point where it sinks into the beach to the south of the town. From 

 its position on the shore I judge that it occupies extensive hollows 

 in the ' Basement ' Clay. Towards its junction with that mass 

 small pebbles make their appearance, otherwise it is remarkably 

 free from any foreign admixture. 



The beds which immediately underlie this laminated clay, on 

 both the North and South Shore, are those to which I would more 

 particularly draw attention on account of their near relationshijD to 

 the mass of sand and shells known as the Bridlington Crag, which 

 evidently forms part of this division. 



Lithologically, they consist of a dark sandy, sometimes earthy 

 clay, of a dark greenish-blue colour when damp, but having a more 

 decidedly green tinge when dried. The pebbles contained in it are 

 chiefly small, and consist of fragments of rocks from strata exposed 

 along the coast to the northward, being derived principally from the 

 Lias, Oolite and Chalk, with an occasional fragment from the 

 Septarian nodules of the Speeton Clay, and with others from rocks at 

 far greater distances. On the whole, it is not nearly so pebbly as 

 the ' Purple ' Clay, for although in some patches pebbles are very 

 plentiful, in others they are nearly absent. In one or two places 

 there appear in it what have evidently been at some time masses of 

 chalk ; but these are now so crushed and disintegrated as to re- 

 semble streaks of rough pipe-clay. 



These sandy clays form the top of beds which I identify as 

 ■the ' Chalky ' or ' Basement ' Clay of Messrs. Wood and Eome. 

 On referring to their paper,^ the reader will find that these gentlemen 

 only extend this division as far north as Skipsea, doubtless never 

 having witnessed the exposure of the beds on the South Beach 

 which lie just above the extreme low- water mark of spring tides, 

 consisting of the same ' leaden-coloured ' clay, and characterized by 

 nearly the same abundance of chalk as the ' Basement ' clay 

 described by them as occurring further south. 



It is in the above-mentioned sandy clays on the South Shore that I 

 have found the shells in question in the greatest abundance, though 

 I have also actually obtained them from the ' Basement ' clay itself. 



Bearing in mind the marked distinction observable between the 

 ' Basement ' clay and the ' Purple ' clay, exhibiting, as I think, a 

 distinct alteration of some kind in the nature, and possibly in the 

 direction of the glacial action, I was very much surprised to find 

 that actually in the Purple clay itself, and at heights varying up to 

 twenty feet above the horizon of the sandy bed already described, 

 there were to be seen fragments of the very same shells mixed up 

 with its mass, and included in the debris gathered in by the glacial 

 action which deposited this clay. It was these fragments of shells 

 which I first discovered in 1874, and which attracted my attention 

 to the subject at a time when the ' Bridlington Crag ' deposit was 

 wholly invisible. 



Having identified the fragments in the ' Purple ' clay with the 

 shells found in the ' Basement ' beds, I was led to follow up the 

 1 Quart. Journ. Geol. Soc. vol. xxiy. p. 170. 



