MODIFIED DRIFT ALONG CONNECTICUT RIVER. 25 
Waterford we find irregular hillocks of sand, barren of vegetation, and 
drifted by the wind, the highest of which are about 200 feet above the 
river. Below this point the modified drift rises in irregular slopes to a 
height of 200 feet in several places, and its position shows it to have been 
principally deposited from currents of the main valley. As we approach 
the foot of the falls its coarse character is changed, and sand predomi- 
nates in the place of gravel. These deposits probably once filled this 
part of the valley nearly 200 feet above the present river, sloping in six 
miles between Lower Waterford and Passumpsic river from about 800 to 
650 feet above the sea. 
The course of the river along Fifteen-miles falls is S. 70° W., being 
turned much to the west from its general direction. This course is at 
right angles to the line of motion of the great ice-sheet; consequently 
this valley was sheltered from the direct grooving and rasping of the ice, 
and must be supposed to have furnished a lodgment for much of the 
ground-moraine or till that accumulated in its track, We have men- 
tioned that this material forms the river channel, nearly everywhere con- 
cealing the underlying rocks. It also forms the sides of the valley for 
most of the way, rising quite steeply from the river, and sometimes pre- 
senting a terraced appearance at a height much above the present chan- 
nel. These considerations lead to the conclusion that the river has 
excavated much of its present deep, narrow channel through this till 
since the disappearance of the ice, and since the deposition of its highest 
modified drift. 
The facts observed point to an order of events somewhat as follows: 
In the ice-age a great amount of till was caught by the transverse valley. 
At the melting of the ice modified drift was swept into the valley, mass- 
ing in the largest quantity at its lower end, and deltas were deposited by 
tributary streams. In some places the wind seems to have blown up 
sand-drifts to a position on the hillside above the normal height of modi- 
fied drift. As soon as the melting had receded to a few miles above the 
head of these falls, further deposition ceased, all the material supplied 
being retained in the upper valley. The river next began the work of 
excavation. Most of the modified drift was carried away, and considera- 
ble depths channelled out in the till. It does not appear certain that a 
great amount of till was removed from the head of the falls; at least, 
VOL. III. 4 
