Chap. VI. AIDED BY WORMS. 273 



tides of the chalk were found three inches 

 below the casting. The experiment was re- 

 peated on three other castings on different 

 parts of the lawn, which sloped at 2° 30', 

 3° an-d 6°; and particles of chalk could be 

 seen between 4 and 5 inches below the cast- 

 ing ; and after the surface had become dry, 

 particles were found in two cases at a distance 

 of 5 and 6 inches. Several other castincfs 

 with precipitated chalk placed on their 

 summits were left to the natural action of 

 the rain. In one case, after rain which was 

 not heavy, the casting was longitudinally 

 streaked with white. In two other cases the 

 surface of the ground was rendered some- 

 what white for a distance of one inch from 

 the casting ; and. some soil collected at a dis- 

 tance of 2^ inches, where the slope was 7°, 

 effervesced slightly when placed iu acid. 

 After one or two weeks, the chalk was wholly 

 or almost wholly washed away from all the 

 castings on which it had been placed, and 

 these had recovered their natural colour. 



It may be here remarked that after very 

 heavy rain shallow pools may be seen on level 

 or nearly level fields, where the soil is not 



