PART IV. 



AGRICULTURE. 



207 



made to preserve bold shores which are apt to be washed away or 

 undermined by the action of water ; for they have seldom been 

 properly built with mortar, and pointed with strong cement, or 

 built with hewn stone very neatly jointed, either of which are 

 sufficiently durable. Notwithstanding these general censures on 

 embankments, however, there are numerous instances in which 

 they have answered the purpose in the most satisfactory man- 

 ner. Those made of earth, in some places in England, are 100 

 feet broadband only 12 or 14 feet high; and these have always 

 been proof against the tides. Some quays are built with mor- 

 tar * made from powdered unburnt limestone and coarse sand, 

 and pointed with puzzolana earth ; and these resist the sea like 

 solid rock. But the general errors which I have noticed, have 

 been sufficient to raise numberless objections against the com- 

 mon mode of making embankments, and have also deterred, 

 many from attempting to gain land from the sea. 



* A water cement, or mortar that hardens underwater, has been formed, by 

 mixing four parts of blue clay, six of black oxyde of manganese, and nine of carbo- 

 nate of lime ; this mixture, after being submitted to a white heatj is mixed with sixty 

 parts of sand, and water sufficient to form it into mortar. At Dorking, Surrey, 

 is found the limestone used for the West-India and WappingDocks, which has been 

 considered as capable of forming the most durable mortar of any in this country „ 



