BRUSH AND ROCK DAMS. 221 



earth, brush, and logs may be made to answer the pur- 

 pose. There can be no better principle of construction 

 adopted for such dams, than that made use of instinct- 

 ively by those sagacious dam-builders, the beavers, whose 

 works, able to withstand floods and freshets, easily made 

 and easily repaired, last for ages, and mock in their simple 



Fig. 103. BBUSH AND LOG DAM. 



strength many of our best engineering works. These 

 dams have a foundation of mud and brush, which bind 

 together very intimately ; the brush always being laid with 

 the buts down stream, arrests all floating or suspended 

 matter which is brought down with the current, and thus 

 adds daily and constantly to the material, and the 

 strength of the dam. Into this brush is interwoven logs 

 and sticks, limbs and stems of trees, and stones, so placed 

 that the pressure of the water tends to hold them down, 

 and the interstices are filled in with earth which is also 



Fig. 104. DAM OP PILES AND BOCK. 



thrown upon the submerged ends of the timbers. For 

 dams of no greater hight than a few feet, and of a length 

 of from 50 to 100 feet, there is none more simple, useful, 

 economical, and permanent than this. For streams the 

 bottoms of which are soft, sandy, mucky, or muddy, this 

 style of dam has no superior. A section of a dam of this 



