E. Hull — General Relations of the Drift Deposits. 299 



bed/ accompanied by intense cold and the formation of extensive 

 sheets of land-ice. (2) The second resulted in a general depression 

 of the land,2 with the return of a milder climate ; (1) and the third 

 was characterized by a partial re-elevation of the submerged land, 

 and a partial return of a cold climate, productive of local glaciers 

 and icebergs. This period gradually gave place to the climate of 

 our own day, and its change is indicated by the retreat of the glaciers 

 amongst the "Centres of Dispersion," as graphically described by Mr. 

 de Eance, on a recent occasion, in Cumberland, and by Prof. Eamsay, in 

 North Wales. These stages may thus be expressed in a concise form, 

 as I have attempted to show in the accompanying page, on which I 

 have only to remark that the changes from one stage to another are 

 not to be regarded as sudden or abrupt ; between each there was 

 doubtless a period more or less extended, and partaking of the 

 climatical condition of the preceding and succeeding stages ; while 

 the change from the third stage into the recent period is also to be 

 regarded as of a gradual character. 



Tabular View. — Intended to show the Physical Characters of the Three Stages 

 of the Drift period over the British area. 



PERIOD. 



STAGE. 





Upper 



Post- 





Pliocene 



Middle 





or Inter- 



or 



Glacial. 



Drift. 







Lower 



Partial re- eleva- 

 tion as compared 

 with the middle 

 stage, but par- 

 tial submersion 

 as compared with 

 the present day. 



Greatest De- 

 pression : 



Submersion to 

 a depth of 1,300 

 feet E. of Ire- 

 land, 1,400 feet 

 Wales, 1,200 ft. 

 Cumberland, 

 compared with 

 present levels. 



Greatest eleva- 

 tion; 

 Portions of ex- 

 isting seas being 

 then land, and 

 covered by ice. 



CHARACTER OP DEPOSIT. 



ON PLAINS. 



Upper 



Boulder-clay 



(generally 



Marine). 



Shelly Marine 



Sands and 



Gravels. 



(" Limestone 



Gravel" of 



Ireland.) 



Lower 

 Boulder-clay 

 of Scotland, 

 the North of 

 England, and 

 a large por- 

 tion of Ire- 

 land, due 

 chiefly to 

 land-ice. 



ON MOUNTAINS. 



Local 

 Glaciers pro- 

 ducing Ice- 

 bergs and 

 M oraines, 

 etc. 



Mountains 

 reduced to 

 small Archi- 

 pelagos, as 

 shown in 

 Lyell's "An- 

 tiquity of 

 Man," p, 276. 



Perennial 

 snow and ice. 



Changing from 



Arctic 

 to Temperate. 



For the most 

 part temperate. 



Arctic. 

 The general 

 surface of the 

 Northern por- 

 tions of the 

 British Isles, 

 including Ire- 

 land, resemb- 

 ling Greenland 

 at the present 



^ Possibly to the extent represented by Lyell in his work on " The Antiquity of 

 Man," p. 279. ^ To the extent shown by map, p. 276.— Uid. 



