1894- 
203 
[Wood worth. 
now set forth. If in a channel at the base of a stagnant and dis- 
appearing glacier, detritus be laid down with a constructional 
surface relatively even, but with a width varying within short 
distances, so that at one point the width is less than the thick- 
ness, and at another point greater than the thickness of the 
deposit, the ultimate crest-line of the deposit, when the ice melts 
away, will vary. The caving of the sides will produce slopes 
whose intersection will take place above the coQStructional 
surface where the deposit is wider than it is high in the ratio of 
one to one and one half (about). Where this ratio or a greater 
one obtains, the constructional surface along its median line will 
not be lowered. Where the thickness is equal to or exceeds the 
width of the deposit, there the slopes will intersect below the 
constructional surface and bring down the crest-line beneath the 
original surface. The average slope may be assumed to be 30°. 
Where this readjustment has taken place, it follows that an esker 
channel was originally narrow where the esker is now low, and 
wide where the esker is high. This gravitative rearrangement of 
the crest-line would not be produced in deposits whose thickness 
did not equal or exceed the width of the channel. The applica- 
tion of this ])rinciple to variations of crest-line is made possible 
by the uniform limitation of eskers to a cross-section within the 
range of this action. It is needless to enumerate examples in 
which the sharp ridge-like cross-section is the prevailing topo- 
graphic feature for extensive segments of eskers. The annexed 
diagrams illustrate the geometrical principles involved in this 
explanation. The interpretation of this feature as observed in 
the Auburndale esker will be considered below. 
Fig. 1. 
Fig. 2. 
In these figures A B C D represents the assumed cross-section of the 
gravels and sands deposited in a tunnel of varying width before the ice 
has melted from the sides. E F G represents the cross-section after the 
sides of the original dei)osit have slidden down. In Fig. I, F is above the 
constructional height, and the crest-line is there unchanged; in Fig. 2, F 
is below the constructional height and the crest is lowered. 
