ENCLOSING DAMS. 65 



about two feet of sand and shells overlying hard blue clay. 

 The abutments and a portion of the piling at each end were 

 upon the rock. 



The gauge-piles were driven into the clay about 12 feet, 

 and the filling pilea about 8 feet. The tops of the two outer 

 rows were kept at 7 feet above high- water level. They were 

 spaced 7 feet 6 inches apart, and were secured together by four 

 tiers of IJ-inch through-bolts screwed up on whole-timber inside 



FIG. 48. 



and outside walings. The space between the piles was cleared 

 of all sand and loose material, and filled in with well-rammed 

 puddled clay. 



The inner row of piles was driven 10 feet 3 inches to the 

 rear, the heads being about 3 feet above the low- water level ; 

 the heads were secured with inside and outside whole-timber 

 walings, and connected with the second row of piles by half- 

 timber double horizontal struts and 2-inch through tie-bolts. 

 Whole-timber raking shores were fixed from the top of the inner 



F 



