320 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
level did not fall so much as to drain the valley. After successive 
drops in the level of the lake the head of the valley would be above 
water and thus subject to river erosion. One of the later stands of 
the lake might last long enough to allow the inflowing river to grade 
its course, build a delta and develop flood-plains. While the river 
was at grade, a large part of the valley filling might be removed by 
lateral swinging of the river. ‘Thus only flanking terraces would be 
left to mark the former lake-levels. Let the lake-level to which the 
river is graded drop again. The river would be permitted to partly 
consume its former flood-plains and develop new ones. 
Now, if, to the history so far outlined, there are added two com- 
plications, namely :— that instead of one valley there are three parallel 
valleys, which during certain periods of the ice retreat were inter- 
communicating, and that during this glacial history and subsequently 
there has been tilting of the land on which the records of the lake- 
levels have been made, then the chief conditions which have obtained 
in the western Vermont valleys will be recorded. 
THe Winooski Bastn.— Side Valleys. One of the first lakes to 
form in front of the ice in the Winooski basin was north of the swampy 
divide, at an altitude of 990 feet, between the Dog River which is one 
of the southern tributaries of the Winooski River, and the Third 
Branch of the White River, which is tributary to the Connecticut 
River. 
Extending north from the divide at Roxbury, there is a sand-plain 
which rises northward to a height of 20 feet above the divide, where 
it joins an esker about one third of a mile long. On the east side of 
the head of the sand-plain an ice-block hole has a delicately marked 
shore-line about its rim. Such a line may be ascribed to lake ice 
action along the shore, rather than to waves. 
A massive sand terrace which appears 2 miles north of Roxbury 
on the east side of the railroad at an elevation of 975 feet was probably 
built in a marginal lake. 
Three deltas, further down the Dog River valley, in the vicinity of 
Northfield, at an elevation of 940 feet, were all possibly built into one 
lake. One delta is at the mouth of a tributary entering the Dog 
River from Northfield Centre, another is east of the Northfield railroad 
station at the mouth of a small brook, and the other is one and one 
half miles south of Northfield on the east side of the river. 
Two and one-half miles south of Northfield terraces, which are 
gravelly, occur on the sides of the valley at heights of 845, 830, 820 feet 
above the sea. They were probably cut by streams marginal to 
