MORAINES OF RECESSION 431 
years. The diameter A C may be taken to represent the amplitude 
of the oscillation of the ice-front as affected by the precessional 
oscillation of climate, and is put at thirty miles. Of course the 
ice keeps melting as it moves forward so that there is no material 
thing that constantly accompanies the ice-front as it changes its 
position. But we may imagine a point which shall keep its 
place constantly at the front edge. This point would move to 
Cold 
and fro with the ice-front on the line A C, following the order 
of the precessional changes of climate. An arrow within the 
circle shows the direction of the general glacial flow, which is 
maintained in the glacier itself through all phases of advance 
and retreat of the ice-front. The climaxes of cold will therefore 
be at A and the climaxes of warmth at C, and the ice-front will 
have a period of rest at each of these points. When the ice- 
front passes O it will always be moving at the maximum rate, 
whether of advance or retreat. As the ice-front moved forward 
from O to A its rate of advance would decrease, and would 
become very slow on approaching near to A, and the retreat 
