PLEISTOCENE FORMATIONS OF SANKATY HEAD 729 



A. portlandica at the present time is more limited in its range 

 than A. quadrans, and is somewhat rare. 



From the fact that A. sankatyensis occurs only in the "upper 

 shell bed," where it is quite common and associated with arctic 

 species, it seems probable that it has a very northern range, or is 

 a form which has died out, and is not represented among recent shells. 



Fig. 11 



INTERPRETATION 



It has been thought that these fossiliferous beds at Sankaty Head 

 were made up of old material redeposited; that the last or Wisconsin 

 ice-sheet, moving across the sea-floor, had torn up and transported 

 a quantity of material from old beds lying beneath the sea, and 

 redeposited it in the present position near the ice margin. A notable 

 case of this kind is found in the deposits containing marine fossils 

 which are found on the flanks of Mount Snowdon in Wales, and 

 which owe their elevated situation to the movement of the great 

 Irish Sea glacier over the bed of that sea, and the crowding .of its 

 front with its morainal accumulations up onto the highlands of 

 northwestern Wales. 



It may be mentioned in this connection that the line of kame hills 



