Chap. VI. AIDED BY WOKMS. 271 



as in the tropics, tlie castings appear, as 

 might have been expected, to be washed 

 down in a greater degree than in England. 

 Mr. Scott informs me that near Calcutta the 

 tall columnar castings (previously described), 

 the diameter of which is usually between 1 

 and 1^ inch, subside on a level surface, 

 after heavy rain, into almost circular, thin, 

 flat discs, between 3 and 4 and sometimes 5 

 inches in diameter. Three fresh castings, 

 which had been ejected in the Botanic 

 Gardens " on a slightly inclined, grass- 

 '* covered, artificial bank of loamy clay," were 

 carefully measured, and had a mean height 

 of 2*17, and a mean diameter of 1*43 inches ; 

 these after heavy rain, formed elongated 

 patches of earth, with a mean length in the 

 direction of the slope of 5*83 inches. As the 

 earth had spread very little up the slope, a 

 large part, judging from the original diameter 

 of these castings, must have flowed bodily 

 downwards about 4 inches. Moreover some 

 of the finest earth of which they were com- 

 posed must have been washed completely 

 away to a still greater distance. In drier 

 sites near Calcutta, a species of worm ejects 



