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XXXV. — On the Formation of Mould. 

 By CHARLES DARWIN, Esq., F.R.S., Sec. G.S. 



[Read November 1, 1837.] 



The formation of the superficial layer of earth, commonly called vegetable 

 mould, offers some difficulties in being fully understood, which apparently have 

 been overlooked. In old pasture lands, the mould, to the depth of a few^ 

 inches, differs but slightly, although resting upon various kinds of sub-soil. The 

 uniform fineness of its particles is one of its chief distinguishing characters; 

 and this may be well observed in a gravelly country, where a recently ploughed 

 field immediately adjoins another, which has long remained undisturbed for 

 grazing. In the latter, not a pebble will be seen, either on the surface or im- 

 mediately below it ; although in the ploughed field, a large proportion of the 

 soil may be composed of small stones. From the prevailing use of the ex- 

 pression " vegetable mould," it would appear that its origin is generally at- 

 tributed to some effect of vegetation ; yet it is scarcely conceivable that the 

 turf, in the case of the two adjoining fields, can have produced so remarkable 

 a difference as that alluded to. 



My attention was called to this subject by Mr. Wedgwood, who showed 

 me, whilst I was staying at Maer Hall, in Staffordshire, several fields, some of 

 which a few years previously had been covered with lime, and others with 

 burnt marl and cinders. These substances, in every case, were buried some 

 inches beneath the turf. In several parts of three grazing fields, I dug square 

 holes, and obtained the following results : — 1st. In some good pasture land 

 which had been limed, without having been ploughed, about ten years 

 before, the turf, or the layer in which the roots of the grasses are closely 

 woven together, was about half an inch thick. At two inches and a half be- 

 neath this, or about three from the surface, a layer of lime, or a row of small 

 aggregated lumps of it, formed a well-marked white line around the holes. 

 The soil beneath this layer of lime was gravelly, or of a coarse sandy nature, 

 and differed considerably from the mould nearer the surface. About three 

 years ago cinders also had been spread on this field ; but when I examined 

 it, they were buried at the depth of one inch. They were not sufficiently nu- 

 merous to form a layer, though a line of black spots could clearly be traced 



