DEPOSITS OF THE SUSSEX COAST. 3J:7 



were derived, and their mode of transport ; 4tb, the stratigraphical 

 position of the deposit containing large erratics, whether above or 

 below the marine clays with southern mollusca ; 5th, the character 

 of the fauna and flora found in the several deposits ; 6th, and lastly, 

 what succession of events and what variations of climate are indi- 

 cated by the evidence now collected? Many other questions inci- 

 dentally arise, but these I propose merely to allude to briedy in the 

 present paper, which is mainly confined to the area minutely 

 examined during the past seven years. 



The mode of origin of the Coombe Rock and of the dry Chalk valleys 

 has been dealt with, but since the paper on that subject was published 

 I have examined large additional areas in the South Downs. This 

 work thoroughly bears out the conclusion already arrived at — that 

 the erosion of the valleys, and the deposition of the eroded material 

 in the form of widespread sheets of angular chalky detritus, resulted 

 from the fall of summer rain on a shattered surface of Chalk, ren- 

 dered impervious by freezing during a winter of Arctic severity. 



The second question, "What is the true succession of the deposits? 

 I have nob before dealt with, except that in the discussion on a 

 paper by Mr. A. Bell I drew attention to the fact that erratics are 

 not confined to strata above the mud-deposit of Selsey, and that the 

 period of floating ice was not only earlier than the Coombe Rock, 

 but earlier than the underlying clays with southern shells.^ The 

 only way to show what is the true succession will be to describe the 

 newly exposed sections in Selsey Bill. This must be done in some 

 detail, for on the accuracy of the observations depend, not only the 

 conclusions as to the succession of the deposits, but also our view 

 as to the occurrence or non-occurrence of an interglacial or mild 

 episode during the Pleistocene period in the South of England. 



During the year 1885 I stayed at Chichester, Bognor, and Selsey, 

 and succeeded in examining the marine clays with Chiton sicidus, 

 and also the borings of PJioIas crUpata, but the sections were not 

 extensive, and I came across only one erratic block in the clays. 

 This block was, however, sufficient to show that the dispersal of 

 some, at least, of the erratics dated back to the period when the 

 marine claj's were being deposited, or was still earlier. To the 

 view that the two were contemporaneous there was this objection : 

 the fauna of the clay was distiiictly southern, and showed a sea at 

 least as warm as the present English Channel ; whereas, to allow 

 of ice floating for a sufflcient length of time to carry erratics long 

 distances, the water must be near the freezing-point. Therefore it 

 seemed evident that the marine clays must be newer than the de- 

 posit in which the erratic blocks were first dropped. I have taken 

 every opportunity during the past seven years to search for evidence 

 of this problematic earher glaciation, but it was not till last October 

 that new exposures enabled me to fill up the gap in the series, and to 

 discover the glacial deposit in place. As this erratic-gravel is 

 the oldest Pleistocene deposit yet discovered on the Sussex coast, 

 it will be the first stratum to be dealt with. 



^ Quart. Journ. Geol. Soc. toI. xlvii. (1891) Proc. p. 173. 



