Chap. VI. AIDED BY WORMS. 269 



before rain ; so that the above results are 

 thus far exaggerated. On the other hand, 

 during rain much of the finest earth is 

 washed to a considerable distance from the 

 castings, even where the slope is an ex- 

 tremely gentle one, and is thus wholly lost 

 as far as the above calculations are concerned. 

 Castings ejected during dry weather and 

 which have set hard, lose in the same 

 manner a considerable quantity of fine earth. 

 Dried castings, moreover, are apt to disinte- 

 grate into little pellets, which often roll or 

 are blown down any inclined surface. There- 

 fore the above result, namely that 2*4 cubic 

 inches of earth (weighing 1*85 oz. whilst 

 damp) annually crosses a yard-line of the 

 specified kind, is probably not much if at all 

 exaggerated. 



This amount is small ; but we should bear 

 in mind how many branching valleys inter- 

 sect most countries, the whole length of 

 which must be very great ; and that earth is 

 steadily travelling down both turf-covered 

 sides of each valley. For every 100 yards in 

 length in a valley with sides sloping as in the 

 foregoing cases, 480 cubic inches of damp 



