482 



PLEISTOCENE. 



It is obvious that we cannot precisely mark off all the records of 

 the Quaternary era into the two divisions previously noted. Many 

 Caverns contain Pleistocene as well as Recent deposits, and there 

 may be marine deposits of both ages, which it would be incon- 

 venient to describe separately. Hence the descriptions of the 

 Quaternary phenomena will be arranged mainly according to 

 method of formation, as follows : — 



Marine. 



Terrestrial. 



Eecent, etc. 



Recent 

 and 

 Pleistocene. 



Alluvial (Fluviatile, Recent 

 Lacustrine and and 



Estuarine). Pleistocene. 



Glacial. Pleistocene. 



( Raised Beaches, Shingle Beaches, and 

 ) other Marine deposits. 



(Soils and Kainvvash. 

 Blown Sand. 

 Caverns and Cavern-deposits. 

 V Springs and Tufa. 

 i Alluvium, including Peat, Submerged 

 Forests and River-deposits (Valley 

 gravel, brickearth, etc.), Scrobicularia- 

 clays, etc. 

 Boulder Clay, Gravel, etc. 



PLEISTOCENE. 

 GLACIAL BEDS. 



The Glacial Period may be regarded as including the records of 

 all deposits from the close of the Pliocene period to the com- 

 mencement of Recent times, but strictly speaking the Glacial 

 deposits are those more immediately connected with the agency 

 of ice. These deposits include wide-spread accumulations of 

 Boulder Clay, Loam, Gravel and Sand. The Boulder Clay is more 

 especially due to the direct influence of ice, but associated with it 

 are deposits which may be due to the melting of ice-sheets, or 

 which may have been formed in areas subject to the influence of 

 coast-ice, and ice-bergs. Thus the term Glacial Beds refers to 

 age rather than to particular methods of formation. The Cavern- 

 and River-deposits and the Raised Beaches, which may have been 

 accumulated during the Glacial period, will be noticed separately. 



It must be borne in mind that this Glacial Period, or ' Great Ice Age,' was not 

 necessarily the most important Glacial period that has occurred during geological 

 limes. Dr. CroU has stated his opinion that these periods of intense cold were 

 periodical : we have indications of transport by ice agency in the Chalk period ; 

 and in Permian times there are some (doubtful) evidences of Glacial deposits. 

 (See also p. 36.) The accumulations, however, that evidence the Post- Pliocene 

 Glacial period are the most extensive of the kind that have been preserved, for 

 subsequent changes have not been of sufficient magnitude to obliterate them. 



Attention was drawn in 1840 by Agassiz and Buckland to the 

 evidence of the former existence of glaciers in the British Islands. 



Dr. Buckland's attention was first directed by Prof. Agassiz, in 1S3S, to the 

 phenomena of polished, striated, and furrowed surfaces, and also to the transport 



