Stone Prer to protect STRUCTURE. 411 
Satmon Leaps. 
the mill-power; but upon large rivers the plan is impracti- 
cable. The same principle can be applied to a pass which is 
imperfect, and it has been found to answer. A curving pier 
has been built out from the dam below, so that the water 
falling over the dam is thrown back by it, and though it is 
open at one end, yet it passes far enough across the bed of 
the river just below the fall to so raise the water that fish 
get a start to leap the dam. To increase the depth of water 
between this pier and the dam, a large beam of wood, in slant- 
ing direction from the top of the dam to the pier, conducts a 
wide sheet of water from the top of the dam to between the 
dam and the pier. This method for a salmon-leap can not 
injure the water-power. In all cases, the importance of such 
vital means of assistance to the salmon requires that the arch- 
