HYDROLOGY OP NEW YORK 



GG7 



the river is Potsdam sandstone, the strata dipping at an angle 

 of about 30 degrees downstream. The banks are of sandstone, 

 nearly perpendicular, and about 375 feet apart up to a level of 

 10 feet below the crest of the dam. 



The material for the construction of the masonry work was 

 obtained from quarries near-by, It is Potsdam sandstone which 

 comes out from the quarry with nearly level beds, and no cutting 



was done except to level the crest of the dam after the stone was 

 in place. For the downstream face of the dam stones from 12 to 

 18 inches in thickness, 2 to 4 feet wide and 3 to 1 feet long, were 

 used, the beds being laid normal to the surface. For the upstream 

 face a rubble wall about 3 feet thick was laid of smaller stone. 

 The space between was filled with large bowlders and irregular 

 shaped quarry stones, with concrete rammed in around and be- 

 tween. This dam was completed in the fall of 1899 and has had 

 4y 2 feet of water over its crest in two different seasons. The dam 

 is perfectly water-tight. 



Fig. 44 Cross-section of dam at Hannawa Falls. 



