576 



agency so trivial as it, at first, might be thought ; the great number of 

 earth-worms (as every one must be aware, vi^ho has ever dug in a 

 grass-field) making up for the insignificant quantity of work which 

 each performs. 



On the above hypothesis, the great advantage of old pasture land, 

 which farmers are always particularly averse from breaking up, is ex- 

 plained ; for the worms must require a considerable length of time 

 to prepare a thick stratum of mould, by thoroughly mingling the ori- 

 ginal constituent parts of the soil, as well as the manures added by 

 man. In the peaty field, in fifteen years, about three inches and a 

 half had been well digested. It is probable, however, that the process is 

 continued, though at a slow rate, to a much greater depth ; for as often 

 as a worm is compelled by dry weather or any other cause to descend 

 deep, it must bring to the surface, when it empties the contents of 

 its body, a few particles of earth. The author observed, tliat the diges- 

 tive process of animals is a geological power which acts in another 

 region on a greater scale. In recent coral formations, the quantity 

 of stone converted into the most impalpable mud, by the excavations 

 of boring shells and of nereidous animals, is very great. Nume- 

 rous large fishes (of the genus Spams) likewise subsist by brovssing 

 on the living branches of coral. Mr. Darwin believes, that a large 

 portion of the chalk of Europe was produced from coral, by the 

 digestive action of marine animals, in the same manner as mould has 

 been prepared by the earth-worm on disintegrated rock. The au- 

 thor concluded by remarking, that it is probable that every particle 

 of earth in old pasture land has passed through the intestines of 

 worms, and hence, that in some senses, the term " animal mould" 

 would be more appropriate than " vegetable mould." The agricul- 

 turist in ploughing the ground follows a method strictly natural ; and 

 he only imitates in a rude manner, without being able either to bury 

 the pebbles or to sift the fine from the coarse soil, the work which 

 nature is daily performing by the agency of the earth-worm*. 



* Since the paper was read Mr. Darwin has received from Staffordshire 

 the two following statements : — 1. In the spring of 1835 a boggy field was 

 so thickly covered with sand that the surface appeared of a red colour j but 

 the sand is now overlaid by three quarters of an inch of soil. 2. About 80 

 years ago a field was manured with marl ; and it has been since ploughed, 

 but it is not known at what exact period. An imperfect layer of the marl 

 now exists at a depth, very carefully measured from the surface, of 12 inches 

 in some places, and 14 in others, the difference corresponding to the top 

 and hollows of the ridges or butts. It is certain that the marl was buried 

 before the field was ploughed, because the fragments are not scattered 

 through the soil, but constitute a layer, which is horizontal, and therefore 

 not parallel to the undulations of the ploughed surface. No plough, more- 

 over, could reach the marl in its present position, as the furrows in this 

 neighbourhood are never more than eight inches in depth. In the above 

 paper it is shown, that three inches and a half of mould had been accumu- 

 lated in fifteen years; and in this case, within eighty year? (that is, on the 

 supposition, rendered probable from the agricultural stateof this part of the 

 country, that the field had never before been marled) the earthworms have 

 covered the marl with a bed of earth averaging thirteen inches in thick- 

 ness. 



