PLIOCENE PERIOD IN ENGLAND. 



465 



clay, swept by the severe conditions of climate now approaching 

 into the waters of the sea I am now tracing. In the extreme 

 east of Sheet 68 they thin out to very insignificant thickness before 

 disappearing nnder the beach-line ; and as we approach the mammali- 

 ferous and freshwater bed of Pakefield and Kessingland they dis- 

 appear, setting in again in the condition of beached pebbles and of 

 sands, interstratified and intermixed with pebbles for several miles 

 south of those places, whence southwards to the north-eastern 

 end of the line of fig. I,, and over that line also, the pebbles are 

 absent. The Mollusca of these sands are given in the tabular list to 

 my father's first Supplement to the ' Crag Mollusca ' in the volume of 

 thePalseontographica] Society for 1873, in the column headed "Lower 

 Glacial ;" and to these the researches of Mr. C. Reid have added a 

 few species more, most of which are given in the list accompanying 

 the second Supplement. From a familiarity with the character of 

 purely aqueous deposits, we have long recognized that the uncon- 

 formable stratification which results from false bedding is due to 

 current action ; but our knowledge of the effect produced by the 

 extrusion of morainic material from a glacier which terminates 

 beneath the sea is as yet hypothetical ; nevertheless I believe that 

 the divisions of upper and lower Till separated by sands in this 

 fbrmation of the Cromer coast, which have been made by Mr. 

 Reid, have their origin in the irregular and intermittent extru- 

 sion into the sandy and silty sea-bottom, at the commencement 

 of the stage we are now considering, of material from the land- 

 ice, which having been in existence, as already shown, in the upper 

 waters of the Crag river during Stage I., had by the northerly 

 subsidence of Norfolk which I have described, and by the augmenta- 

 tion of the cold, not only reached the sea in England, but had entered 

 the limits of Norfolk and Suffolk. This material was, in some cases, 

 carried into and interstratified in these sands, and in others pushed 

 over them. Instances of both methods appear in the coast-section of 

 North Norfolk, and in the (chalk) pit at Guist crossed by the line of 

 fig. yill. On no better foundation that I can see have similar 

 divisions of one continuous glacial accumulation been made in other 

 districts and other countries, and a theory of a cycle of alternations 

 from warm to cold climates during the Glacial period evolved to 

 account for them. 



Such, in my opinion, was the origin and mode of accumulation of 

 the pebbly sand and Till as one formation, the structure of which 

 has been greatly obscured by the churning-up which, in common 

 with the Contorted Drift that overlies it, this formation has under- 

 gone, as presently described. Towards the western extremity of 

 the coast-section in Sheet 68, viz. at Weybourne, this churning-up 

 has not taken place ; and there the Till and the Contorted Drift 

 cannot be distinguished, and appear to be one continuous accumu- 

 lation, of which the base is distinctly interstratified with the pebbly 

 sand. At the opposite extremity of the coast-section, a distance of 

 only 14 or 15 miles, this churning-up also ceases ; but there the 

 Till, or what may be considered as representing it, is separated, in 



