STRATIFIED DRIFT 965 



(supermorainic) so far as the ice of that epoch was concerned, 

 exce[)t in so far as forward oscillatory movements intervened in 

 the general period of retreat. So far as such movements inter- 

 vened, their tendency would be to bury or destroy such stratified 

 deposits as were overridden by the temporary advances of the 

 ice, making them intermorainic (inter-till). In a complex body 

 of drift deposited by a single ice-sheet, the edge of which was 

 subject to oscillation, it would not always be possible to tell 

 which beds of intermorainic stratified drift were deposited dur- 

 ing the advance of the ice and which during the retreat, though 

 the latter would of course overlie the former. 



Deposits made by streams as they issued from the ice. — When 

 streams issued from beneath the ice they often made very con- 

 siderable deposits at the point of issue (kames, alluvial fans, etc.) . 

 In case of simple (without oscillation) advance or retreat of the 

 ice, deposits of this sort made during the maximum extension of 

 the ice and during its retreat would remain undestroyed and 

 unburied so far as ice of that epoch is concerned. Those made 

 by the ice at the time of its maximum extension might rest on a 

 driftless surface or on extraglacial stratified drift deposited in 

 advance of the ice, while those made during its retreat would be 

 likely to lie on till. 



The deposits made in this position during the first advance 

 of the ice over any region, were likewise liable to rest on drift- 

 less surfaces or on stratified drift deposited in advance of the ice 

 itself. The advance of the ice was likely to destroy them in 

 whole or in part, and bury what escaped destruction. Stratified 

 deposits made at the margin of an advancing ice-sheet the edge 

 of which was not oscillating are therefore likely to occupy a sub- 

 morainic position, to the limit of ice advance. 



In case the edge of the ice oscillated during its advance, the 

 kame deposits made during a recessional phase of an oscillation 

 might rest on the till of the preceding advance phase. Like- 

 wise the stratified deposits at the edge of the ice during its 

 retreat, commonly, but not universally, rested on till. Mar- 

 ginal deposits of stratified drift made during a recessional phase 



