168 WEIGHT OF EARTH Chap. III. 



house where the lady lived, the castings were 

 not collected at such short intervals of time 

 as those on the terrace ; consequently the 

 loss of fine earth during rainy w^eather must 

 have been greater in this than in the last 

 case. The castings moreover were more 

 sandy, and in collecting them during dry 

 weather they sometimes crumbled into dust, 

 and much was thus lost. Therefore it is 

 certain that the w^orms brought up to the 

 surface considerably more earth than that 

 which was collected. The last collection 

 was made on October 27th, 1871 ; i.e., 367 

 days after the square had been marked out 

 and the surface cleared of all pre-existing 

 castings. The collected castings, after being 

 well dried, weighed 7 '45 3 pounds ; and this 

 would give, for an acre of the same kind of 

 land, 16*1 tons of annually ejected dry earth. 



Summary of the four foregoing Cases. 



(I.) Castings ejected near Nice within about a year, collected 

 by Dr. King on a square foot of surface, calculated to yield per 

 acre 14*58 tons. 



(2.) Castings ejected during about 45 days on a square yard, 

 in a field of poor pasture at the bottom of a large valley in the 

 Chalk, calculated to yield annually per acre 18 "12 tons. 



(3.) Castings collected from a square yard on an old terrace at 



