Davis. 
498 
[May iS, 
was drained away from one side of the esker, the water standing 
at a higher level on the other side might flow over the ridge and 
cut a notch in it. Little emphasis need be attached to this 
explanation until more facts are secured bearing upon it. 
It is manifest that as the ice walls melted away and left the 
sides of the esker unsupported, there must have been more or less 
slipping from summit to base. This would always occur in such 
a manner as to widen the base and narrow the summit of the 
ridge. In case the esker had lain in a channel on the surface of 
the ice, and was afterwards brought down to the ground by the 
melting of the ice by water current percolating beneath the gravels, 
an additional relation of disturbance to form should occur. It 
appears more likely that the middle line of the esker would in 
that case be the more frequent course of the trickling stream be- 
neath it, and hence that as the gravel settled down there should 
be signs of falling in from the upper margin towards the medial 
line. In this case, the faults and dislocations in the gravel would 
have their downthrow towards the axis of the esker until the 
whole deposit had reached the ground ; afterwards as the ice 
walls melted away the faults or slips would fall towards the 
margin. In the other case, they would fall only towards either 
margin. Whether this deductive test between the two conditions 
of esker formations is a complete one or not, I shall not attempt 
to say ; but there is no question that the sections of eskers that 
I have seen accord much more favorably with the latter than with 
he former. The best excavation showing the structure of an 
esker ridge now open to observation is southeast of Newtonville 
station about half a mile distant ; and here the signs of an out- 
ward settlement and dislocation have been repeatedly observed 
during the deepening of the cut in the past four years ; but no in- 
dications of inward slipping have appeared. 
20 . REVIEW AND CONCLUSIONS. 
In conclusion, before reviewing the line of argument here pre- 
sented, I desire to repeat the title of the essay — the subglacial 
origin of certain eskers — in order to assure the reader that I do 
not desire to exclude in the least the open possibility of the 
superglacial origin of other eskers. However it may be else- 
