The water from the weir or gates, falls into a well,, and is then carried off through a culvert to the outside channel. A stone building with a brick arched roof is erected, so as to inclose the waste weir and its appurtenances. Croton Dam. The southern shore of the Croton river at the point where the dam but not is located, is a gneiss rock moderately sloping up the hill from the water's edge, ;

appearing to extend far into the river. The dam required to be raised 40 feet above low

CROTON AQUEDUCT. 207

water in the river and it was an important object to arrange the plan so as to obtain a ;

rock foundation for the masonry. To effect this, the northern abutment was located as far in the river as the rock was supposed to extend, and from this to build up the dam to the level where the top line intersected the natural slope of the hill, and then to cut the hill away; making an opening sufficient for the waste weir of the dam.

In prosecuting the work, it was found the rock descended more rapidly into the river than was supposed, which induced the moving of the abutment further towards the hill than at first located and finally, an artificial foundation had to be made for a small por- ;

tion of it. It was intended to make the waste of the dam 100 feet, with abutments of eight feet high; but in consequence of the disappointment in regard to the extent of the rock in the river, it was found difficult to obtain the desired length of the water way, and it was concluded to raise the abutment to 12 feet at the lower end, and 15 feet at the upper end, and allow the water way to remain an average length of 90 feet for this height.