PLEISTOCENE AND RECENT. 



481 



Thus the chief divisions of the Quaternary era are partly based 

 on physical considerations, and partly on the evidence of the 

 organic remains. It may therefore be useful to give the following 

 summary of the principal changes that appear to have occurred 

 in our country during this era:^ — 



[ The Present. 



Depression bringing about final insu- 

 lation of Britain. Climate humid. 

 Decay of Forests and growth of 

 Peat-mosses. 



Britain again becomes continental. 

 Summer and winter temperatures 

 more excessive than now ; age 

 of great Forests. Incoming of 

 Recent Fauna. 



Retreat of the ice, and period of 



/ small local glaciers on the higher 



mountain-regions, when Britain 



was probably isolated, and land 



of less extent than now. 



Severe glacial conditions, with glaciers 

 and coast-ice, affecting more par- 

 ticularly Scotland, Wales, and 

 the northern districts of England. 



Britain continental with climate 

 changing from intense cold to 

 temperate and genial. Arctic 

 and southern Mammalia visit 

 Britain, according as climatal 

 conditions become suited to their 

 needs. 



Elevation of land, accompanied by 

 intense glacial conditions, with 

 great ice-sheets formed by con- 

 fluent glaciers, extending over 

 large tracts of country. 



Submergence of considerable areas 

 and deposition of marine sands 

 and gravels, etc. 



Elevation of land and severe glacial 

 \^ conditions. 



u \ Indications of approaching cold. 



Alluvium. ^ -i -"^ 



Submerged Forests. "" <^ 



Modern Beaches and Marine 



deposits (Burtle Beds, 



etc.), Blown Sand, etc. \^ d 

 Raised Beaches (in part), I "^ !^ s 



River-gravels, and some 



Cavern-deposits. 



Eskers, Perched Blocks, etc. 

 ' Head ' (subaerial detritus) of south 

 of England (of all ages subse- 

 quent to Pliocene period ?) 



Hessle and Purple Clays of Lincoln- 

 shire, Newer Pennine Boulder 

 Clay, and newest Boulder Clay of 

 N. Wales, etc. ? Erratic beds of 

 Selsea. 



Plateau gravels (in part) ; Raised 

 Beaches (in part). Old River- 

 and Cavern-deposits, with Paljeo- 

 lithic Implements, remains of 

 Manmioth, Rhinoceros, Hyaena, 

 etc. Corbiciila JJtiminalis. 



Marine deposits of March, Kelsea 

 Hill, Nar Valley, etc., with 

 Mammalian remains, etc. Hessle 

 mammaliferous gravel. 



Chalky Boulder Clay. 



Basement-clay of Lincolnshire (with 

 Bridlington shell-bed). 



Upper Boulder Clay (in part) of 

 Lancashire, Cheshire, and Mid- 

 land Counties. 



Middle Glacial Sands of East Anglia. 



Shell)' sands and gravels of Moel 

 Tryfaen, Macclesfield, Black- 

 pool, etc. 



Cromer Till, and earliest Boulder 

 Clays of other parts. 



Cromer Forest Bed and Norwich 

 CrajT Series. 



' This Table is partly based on that given by Prof James Geikie, Great Ice 

 Age, ed. 2, p. 570. The earliest attempt at a Table showing changes during Post- 

 Pliocene times was made in 1853 by J. Trimmer, Q. J. ix. 295 ; see also Ramsay, 

 Phys. Geol. and Geog. Gt. Britain, ed. 5, p. 380 ; Researches in Newer Pliocene 

 and Post-Tertiary Geology, by James Smith of Jordan Hill, 1S62 ; and Ussher, 

 Post-Tertiary Geol. Cornwall, 1879, p. 50. 



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