497 
[Davis. 
1893.] 
to another outlet, leaving both esker and plateau to their fate. 
It must not be supposed that the stream continued after the 
delta had ceased growing. Once made, the structure stood un- 
altered except by insignificant action to the present time. The 
ice withdrew slowly by melting ; the steep delta head then prob- 
ably fell back into the unoccupied space, thus assuming its present 
slope and perhaps producing some of the disordered structure 
obscurely seen in the cut of the Circuit railroad ; but of this little 
can be said until additional excavations reveal the head structure 
more completely. At the same time, the support that was given 
to the sharp-ridged esker was gradually withdrawn on either side, 
and the gravels were allowed to settle to a slope of equilibrium. 
If the water body had already drained away, the slipping down 
on the esker side would proceed more rapidly ; but if the water 
still held its surface at the delta level, the settlement of the esker 
side might progress somewhat slowly. In the eastern part of the 
Circuit cut, evidence of this is afforded in the relations of the 
frontal beds of the sand plain to a buried esker which they over- 
lie. The esker appears to be a feeder of the Newton Lower Falls 
plateau; the sands belong to the Woodland plateau. It is mani- 
fest from the relation of the esker gravels to the plateau sands 
that the former had not completed their lateral settling until 
some at least of the sand beds had been laid upon them ; for the 
two are confused on the buried slope of the esker. This must 
mean that the esker preserved its steep side for the considerable 
time required for the ice front to melt back from the larger New- 
ton Lower Falls plateau to its later position along the head of the 
smaller Woodland plateau; and that during this time the water 
level was maintained at the plateau height, as the two pla- 
teaus stand at the same level. It may be supposed that the 
water level in front of the decaying ice was generally not main- 
tained so long as here indicated ; and in evidence of this earlier 
withdrawal, I may refer to the frequent notching of the feeding 
esker close to the point of junction with the plateau head. This 
has been remarked upon by several observers, although no pub- 
lished record of it exists as far as I know. It may be best 
explained as a result of the discharge of the water body in which 
the delta was built, and not long after it was completed ; or before 
the ice front had melted far back from its head . 1 As the water 
1 This was suggested to me by Baron G. de Geer, of Sweden. 
PROCEEDINGS B. S. N. H. VOL. XXV. 32 SEPT. 1892. 
