

94 
the numerous quiet reaches between the dams, and one stretch 
of rapids. 
One serious obstacle, not foreseen, was the fact that several 
lines of water pipes and large drainage pipes cross the course 
of the brook at numerous points. After various methods of pro- 
tection against leakage into the drainage pipes were tried, it was 
found necessary completely to encase them under the stream and 
for some distance on e‘ther side in concrete jackets. “This proved 
effective against draining off the water from the brook. 
The dams were first constructed of concrete, extending for 
12-18 inches or more into each bank, and for two or three feet 
below the water-level. A large glacial boulder of chosen shape 
was then cemented into most of the concrete bases. and the top 
of these boulders determines the height of the water up stream 
to the next dam. ‘This method of construction is well illustrated 
in figure 15, which shows the dam, number 7, Just above the 
swamp. At some portions of the stream the excavation amounted 
to as much as seven feet (fig. 14). 
bt 
The surface geology along the brook is rather interesting, 
for the stream crosses the boundary between the Harbor Hill 
terminal moraine of the continental ice-sheet and the overwash 
plain lying to the south. The condition south of the moraine 
was much complicated by the fact that the level of the ground 
had been raised by fill, so that cans, bricks, and other material, 
not calculated to add to the imperviousness of the soil, were 
encountered in considerable quantity. 
In excavating south of the edge of the moraine not a stone 
was encountered as large as a man’s head, but north of this line 
large and small boulders were encountered in quantity (fig. 16), 
Some of these boulders were too large to remove (e. g. fig. 14), 
but one of them was of such shape, and lay in such a manner, 
as to form one of the dams (known as No. ie? 
Between the water level of the lake and that of the terminal 
pool of the brook there is a total fall of nearly thirty-six feet. 
As noted in the Recorp for July, 1912, water was turned 
into the brook for the first time on May 27, 1912. During the 
past spring (1913) several changes have been made, including 
the enlargement of the swamp, and of several pools, and minor 
