DEPOSITS OF THE ST7SSEX COAST, 361 



As we travel northwards the deposits of the mild interglacial 

 period seem to be represented by the raised estuarine and fluviatile 

 strata of Clacton, in Essex, with Corhicula Jtuminalis, Unio littora- 

 lis^ &c. In Norfolk we find on the coast at Mundesley a series of 

 loams with Hydrohia marginata and Emys lutaria. These rest in 

 an eroded channel in Boulder Clay and are covered by coarse gravels 

 without fossils. The same period is probably represented in the Een- 

 land by the gravels of March, which contain a somewhat boreal assem- 

 blage of marine moUusca, but are also full of Corhicula fluminalis. 



Still farther north the same assemblage of marine moUusca that 

 characterizes the March gravels is found to lie between two Boulder 

 Clays, but there again it is full of the Corhicula. At Bridlington 

 and Speeton f ossilif erous strata underlie a great thickness of Boulder 

 Clay, but rest directly on Secondary rocks. These strata my friend, 

 Mr. G. W. Lamplugh, is inclined to speak of as ' pre-glacial' ; but 

 after carefully reading his paper ^ and re-examining my notes I 

 still think that the correlation adopted in my memoir on Hoiderness 

 is correct. North of Plamborough Head no trace of this character- 

 istic fauna has yet been found, and the so-called 'interglacial' 

 deposits of Scotland yield so large a proportion of plants generally 

 considered to have been introduced as weeds of cultivation that I 

 cannot help feeling that some mistake has been made, and that 

 landslips or creep have in most cases been the cause of the appear- 

 ance of Boulder Clay above the fossiliferous strata. 



Though the land and freshwater species show little change of 

 climate between south and east, there exists a marked difference in 

 the marine moUusca. In Sussex the marine fossils seem to indicate 

 a sea warmer than the air, while in the Eastern Counties the air was 

 apparently warmer than the sea. This discordance may have been 

 due to the want of connexion between the two seas, but we do not 

 yet know at what date England was separated from the Continent. 



Prom what has been said in the foregoing remarks it will appear 

 that the South and East of England show evidence of two distinct 

 periods of Arctic cold. During the earlier of these periods all Britain 

 north of the Thames was buried under ice, excepting certain 

 nunataJcs, or isolated hills rising through the ice. Then came a 

 mild episode, during which a characteristic mammalian and moUus- 

 can Pleistocene fauna inhabited this country, and southern species 

 of the Cromer Eorest-bed re-appeared. Afterwards, an increase of 

 cold caused a second glaciation of the area north of the Wash, 

 whilst in non-glaciated areas rain falling on frozen soil led to the 

 formation of extensive sheets of gravel. 



DiscTjssioif (on the two peeceding Papers). 



The Peesident gave expression to what he felt sure was the 

 general feeling of regret that continued indisposition again pre- 

 vented Prof. Prestwich from being present at the reading and dis- 

 cussion of his important paper. He also complimented Mr. Heid on 



1 Quart. Journ. Geol. Soc. vol. xlvii. (1891) p. 384. 



