214 



AGRICULTURE. 



BOOK I. 



or stones, defending parts of the banks of rivers, by throwing 

 the current to the opposite side. This naturally leads us to the 

 idea of piers, which are of great use either in defending em- 

 bankments, or the margins of brooks or rivers. In the former 

 case, they may generally be made and coated over with the 

 same material as the embankment itself. In the latter they 

 should be made of stone decreasing every way as they project 

 outwards, as shewn in fig. 9- In both cases, however, they 

 may be composed of brushwood fastened to stakes with much 

 better effect. Frequently a simple fence of rude wicker-work, 

 (called in many places stakes and rice) three or four yards long, 

 will be sufficient. Stone embankments, unless made as shewn 

 in fig. 9., often form eddies below them; but fences of brush- 

 wood cannot operate in this manner. They have the same 

 mild effect in checking the rapidity of water, J;hat a hedge has 

 in softening a current of air. 



In the designing and disposition of piers or projections in 

 rivers, considerable reflection is requisite, to ascertain the proper 

 spot in which they should be placed, and the exact length which 

 they should project into the river : too great a projection en- 

 dangers the opposite bank, and may produce an eddy below 

 fhe pier, and a reverberation from the opposite bank, which 

 will do more harm than if no pier had been built. When the 

 pier is to be built of stone, which is necessary in rivers of rocky 



