OF THE PLEISTOCENE DEPOSITS OF DEVON. 



457 



Period 



Deposits. 



Changes indicated. 



Correspond- 

 ing to 







f Land higher than now, but 



i 



u 



h3 



< 





II. 



sinking. 





s 





Fluviatile period, gravels 



Devon experienced different me- 





h3 



3 





connected with the forma- 



teorological conditions from the 







tion of the present valley- 



present, the streams being of greater 









system, and occupying sites 



volume. 









indicative of its gradual 



Culmination of subsidence at 









elaboration, during which 



from 10 to 60 feet abore the sea- 









the raised beaches were 



level, marked by Baised Beaches. 



/ 







formed, and the "head" ac- 



■ Elevation gradually producing 

 greater cold, more marked seasons, 



\ 







cumulated. 



O 





hi 



? Cave - earth of Kent's 



and searching winter frosts, leading 



"g 





o 



Cavern (in part). 



to much waste of exposed rock-sur- 



(N 





si -i 



? Granular stalagmite of 



faces, floods, &c. 



3 





g 



Kent's Cavern. 



Probable culmination of the ele- 



► "o 





o 



? Clay of Petrockstow in 



vation in continental conditions 



43 ) 



t3 



Ah 



part. 



admitting of the migration south- 





Clay of Rounclswell, near 



ward of a temperate fauna and the 



Pi 





Barnstaple. 



advent of one requiring cold tem- 



8 







perate conditions. 



W. 

 J 





( Most of the valleys excavated 



N 







to nearly their present depths du- 









ring the earlier stages of an ensuing 







III. 



subsidence which led to conditions 







Submarine forests. 



favourable to forest-growth upon 







Most of the river-valley 



the old marine plain and, later on, 







gravels and alluvial tracts 



in inland localities. 







bordering the present river- 



The gradual circumscription of 



"Is 





courses. 



the forest belt, by the advancing sea 



"o 







■{ and diminishing rainfall led to the 









formation of swamps in maritime 







districts. 



O 







The desertion of their old chan- 









| nels by the dwindling streams and 









the excavation of new courses in 









them, whilst the sea finally en- 









tombed the forests and swamps on 







IV. 



the coasts and produced the present 





I 



The present. 



^ cliff-line. 





The Postglacial deposits, as will be seen in the foregoing Table, 

 have been divided into three snb-periods. That these are only con- 

 sidered Postglacial as regards Devon will be seen from the last 

 column, where a rough correlation with the glacial vicissitudes ex- 

 perienced by other parts of Britain has been attempted. 



Unless we regard the clay with flint and chert as the relics of an 

 ice-bed metamorphosed in situ, from which all morainic debris had 

 subsequently been swept away, I know of no signs of the former 

 existence of land-ice in Devon. On the other hand, there is no 

 indication of a glacial submergence. 



Yet the accumulation of the " head " seems to indicate the effect 

 of the last throes of the Glacial epoch (second glacial period) on the 



