432 FRANK BURSLEY TAYLOR 
from A to O would have the same character in reverse order. 
The five miles nearest to dA represents the approximate width of 
the belt in which terminal moraines at the cold climaxes are 
built. If the whole period of precession be 10,000 years and 
the amplitude thirty miles, it is easy to show that the ice-front 
would be within the five-mile belt (60’) about 2700 years, and 
within the three-mile belt (@az’) about 2075 years. A period of 
terminal moraine building of the same duration would also take 
place at C, the warm end of the oscillation, but the moraines 
built there would always be overrun and destroyed at the next 
advance. 
If this process were carried on with ideal simplicity the result- 
ing forms of the terminal moraines at the two extremes of oscil- 
lation would be substantially as represented in cross section in 
the figure. Those at A would have relatively short, steep front 
slopes and long, gentle back slopes, while those at C would have 
long, gentle front slopes and short, steep back slopes. In the 
moraine series as we have it, all those made at C have been 
destroyed, and we have left only those made at A. We shall 
see presently that where the conditions were simplest the 
moraines do in fact show plainly a tendency to take the form 
shown at A. 
If the period of precession were 20,000 years, the amplitude 
remaining the same, the time of the ice-front in the five-mile 
belt would be doubled, or 5400 years. On the other hand, if 
the period were 5000 years the time in the five-mile moraine 
belt would be 1350 years, and in the three-mile belt 1037 years. 
The character of the moraine would also be affected by the 
amplitude of the oscillation, the period remaining the same. 
The amplitude would necessarily vary greatly in different places, 
the chief determining condition being the character of the land 
relief and the relation of the ice to it. Against a steep slope 
towards the ice the oscillation would be greatly reduced and 
the moraines would be closely packed together, as is seen in 
interlobate areas. In wide flat areas, like the Saint Clair-Detroit 
and Maumee valleys, the amplitude would be at its greatest. 
