T. M. Reade — Post-Glacial Geology. Ill 



temperate conditions ; the periods becoming less intensely con- 

 trasted towards the close. ^ This was the time of great continental 

 ice-sheets, but in the later glacial periods of the same cycle the ice- 

 sheets were less extensive. Oscillations of the relative level of land 

 and sea took place, but to what extent is not known.^ 



2nd. A period of unknown duration, when the ice-sheets withdrew 

 from all the low grounds, leaving behind them piles of rubbish. 

 Climate becoming temperate. 



3rd. A period of subsidence, during which the moraines profondes 

 and terminal moraines were much denuded and their remains heaped 

 up into mounds and ridges by the action of the sea. Climate 

 temperate. 



4th. A period of emergence, characterized throughout by arctic 

 conditions; much floating-ice dispersing erratics over the submerged 

 land; accumulation of clays with arctic moUusca; pauses in the 

 upward movement marked by " raised beaches." 



5th. A period of local glaciers in Great Britain and Ireland ; 

 continued elevation of land ; continental condition of our island 

 followed by partial submergence and re-elevation. Climate becoming 

 gradually ameliorated. 



Having now considered the glacial and interglacial deposits, I pro- 

 pose to take up some of those difficult problems which are suggested 

 by the phenomena of the cave deposits and older river gravels of 

 England. It will be seen in the sequel that the facts already adduced 

 bear strongly upon this subject ; indeed, without a clear conception 

 of the succession of events revealed by our glacial deposits, it appears 

 to me that we run some risk of getting into confusion when we seek 

 te decipher the history of post-glacial accumulations. 



V. — The Post-Glacial Geology anb Phtsiogbaphy of West 



Lancashire and the Mebsey Estuaky. 



By T. Mellard Eeade, C.E., 



Associate of tlie Institution of Civil Engineers. 



MY attention having been directed, during the construction of the 

 Main Outfall Sewer at Birkdale, to the Post-Glacial deposits 

 underlying the great plain between Waterloo and Crossens, and 

 having, through the execution of numerous other works in the dis- 

 trict, peculiar advantages for prosecuting investigations in Post- 

 Glacial Geology, I am induced to lay before your readers several 

 interesting facts, and also, as I venture to think, some important de- 

 ductions therefrom. 



With the exception of the superficial sands and gravels and river 



1 The evidence derived from the Glacial deposits of East Anglia -would make it 

 appear that at the beginning of the cycle the arctic and temperate periods were also 

 less strongly contrasted than they subsequently became. 



* I have stated in the text my beliet that the Macclesfield beds and those of Moel 

 Tryfan ought to be referred to the period of great submergence, during which the 

 kame series or esker drift was accumulated ; they are in all probability the equivalents 

 of the high-level shelves of drift met with in Ireland and Scotland, and likewise in 

 North America. 



