FLOATING. 



365 



Black Forest, at Absdach, on the river Wolf. It consists of piles 



boarded over, and strengthened, away from the reservoir, by large 



blocks of stone between which an opening is left for the sluice-gate. 



(y) Masonry- dams. — These are very strongly built chiefly or 



Fig. 20G. 



entirely of large hewn stones. As a rule, however, they are 

 only faced with hewn stones, the interior being filled with 

 rammed broken stones, or with gravel or rough stones imbedded 

 in clay ; buttresses are then required. 



In order to increase their strength, they are frequently made 

 in a regular curved shape, the convex side of which is opposed 

 to the water-pressure, but in that case it must rest on either 

 side on firm rocks, and then resists the pressure of the water 

 like a great vat. 



Fig. 205, shows the plan and elevation of a masonry-dam 



