206 AGRICULTURE. BOOK I. 



to it, (shewn by the dotted line a a, fig. 2.) they may answer 

 very well; but in the situations where they are commonly 

 placed, the sea is very frequently making breaches in them, 

 which are with much difficulty filled up ; and if this work be 

 for a very short time neglected, the whole embankment will be 

 ruined. 



2. As to the materials, it is of less consequence with what 

 the body of the embankment is constructed, provided those 

 used on the surface next the sea be of the proper kind, and 

 that the whole will contain water. Where the slope next 

 the sea is such as shewn in fig. 2., no material, that is not equal 

 in effect to close-jointed pavement, will be complete. Earth, 

 turf, sand, shells, gravel, or common causeway, are all liable to 

 be damaged by the beating of the tide. Causewaying is much 

 inferior to a good coat of gravel. Even though the slope were 

 considerable, still it does not resist the action of the sea. The 

 water enters at the crevices, sinks down among the stones s 

 loosens the clay or earth below, part of it is divided and car- 

 ried off every tide, vacuums are formed below, one small stone 

 sinks from the rest, a larger succeeds (which gives more room 

 for the operation to go on), some of the surface-stones follow, 

 and the sea, now rushing in with violence, soon displaces the 

 rest, and ruins the embankment. This is almost always the 

 case with heads thrown across rivers, or causewayed banks, 



