Chai'. III. BEOUaHT UP BY WORMS. 141 



ated in soil containing vegetable matter, as 

 well as to the humus-acids.* The projecting 

 corners would also, relatively to the other 

 parts, have been embraced by a larger num- 

 ber of living rootlets ; and these have the 

 power of even attacking marble, as Sachs has 

 shown. Thus, in the course of 29 years, 

 buried angular fragments of chalk had been 

 converted into well-rounded nodules. 



Another part of this same field was mossy, 

 and as it was thought that sifted coal-cinders 

 would improve the pasture, a thick layer was 

 spread over this part either in 1842 or 1843 

 and another layer some years afterwards. 

 In 1871 a trench was here dug, and many 

 cinders lay in a line at a depth of 7 

 inches beneath the surface, with another line 

 at a ' depth of 5 J inches parallel to the one 

 beneath. In another part of this field, 

 which had formerly existed as a separate 

 one, and which it was believed had been 

 pasture-land for more than a century, trenches 

 were dug to see how thick the vegetable 

 mould was. By chance the first trench was 

 made at a spot where at some former period, 



* S. W. Johnson, ' How Crops Peed,' 1870, p. 139 



