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THE POPULAR SCIENCE MONTHLY 



full of fragments of burned marl, conspicuous from their red color, 

 fragments of coal-cinders, and a few white-quartz pebbles. Beneath 

 this layer, and at a depth of four and a half inches from the surface, 

 the original black, peaty, sandy soil with a few quartz pebbles was 



Fig. 3. Section, reduced to Half the Natural Scale, of the Vegetable Mold in a 

 Field, drained and reclaimed Fifteen Years previously. A. turf ; B, vegetable mold 

 without any stones ; C, mold with fragments of burned marl, coal-cinders, and quartz-peb- 

 bles ; D, sub-soil of black, peaty sand, with quartz-pebbles. 



encountered. "Here, therefore," says Mr. Darwin, "the fragments 

 of burned marl and cinders had been covered in the course of fifteen 

 years by a layer of vegetable mold, only two and a half inches in 

 thickness, excluding the turf." Six and a half years afterward this 

 field was re-examined, and the fragments were found at from four to 

 five inches beneath the surface, having been covered in that time with 

 an inch and a half more of mold. The average annual increase of 

 thickness for the whole period was -19 of an inch. This was less than 

 the average increase of thickness in some other fields similarly observed, 

 in which the accumulation amounted to *21 and *22 of an inch annu- 

 ally. 



Another field, lying upon the chalk, and sloping rather steeply in 

 one part, which was turned into pasture-land in 1841, was for several 

 years bo thickly covered with small and large flints that Mr. Darwin's 

 sons always called it " the stony field." When they ran down the slope 

 the stones clattered together; and Mr.. Darwin remembers doubting 

 whether he should live to see the larger flints covered with vegetable 



