DRAINAGE. 613 



covered with earth, as before. This mode of drainage, known 

 to the Romans, was introduced into England by Elkington, 

 and was much practised until 1820. It has the advantage of 

 preventing excessive drainage, and may serve its purpose in 

 places to be planted up, until the roots of the plants can 

 themselves drain the soil. 



ii. DURABILITY. 



Brushwood-drains when the fascines are of alder branches 

 will last from 8 to 10 years ; they rot sooner on calcareous 

 soil and last longer on clay. As, however, the plants once 

 forming a thicket themselves drain the soil, and by the use of 

 fascines too much water is not removed, this method is highly 

 advantageous. 



Drains made with stones may last for 50 years, and are 

 therefore preferable, unless temporary drains are sufficient for 

 the purpose. 



iii. VALUE OF THE METHOD. 



Owing to the high cost of this method of drainage, it is 

 used only for permanently wet ground. It is also largely 

 employed for culverts to lead water across roads. 



b. Glazed or Cement Drain-pipes. 



Drain-pipes made of glazed burned clay or cement and of 

 various dimensions are now generally used for culverts; they 

 unite the advantages of rapid drainage and facility for being 

 cleaned, with that of great durability. 



c. Draining Tiles. 

 i. DESCRIPTION. 



Draining tiles are cylindrical tubes of burned clay with a 

 circular section. They are generally 1 to 1J feet long, \ to J 

 inch thick, and their apertures 1J to 4J inches across. A 

 good draining tile should be well-burned and smooth within, 

 it should ring when struck, show a clean uniform fracture, and 

 stand sudden changes of temperature without cracking, for 

 which it may be tested by plunging it alternately into hot and 



