. Elementary lessons in the physics of agriculture . ^ f> o '^â o â 'iMMl/Z'/MMmm,/ Fig. 35. Section reduced to half natural scale, of the vegetable mould m a field drained and reclaimed 15 years before. Showing turf, vegetable mould without stones, mould with fragments of burnt marl, coal cinders and quartz pebbles; and subsoil of black peaty sand with quartz pebbles. After Darwin. 148. Soil Removal.âPitted against these processes of growth there is a powerful and universal set of agencies con- stantly operating everywhere to transport from higher to lower levels and from the land to the s
. Elementary lessons in the physics of agriculture . ^ f> o '^â o â 'iMMl/Z'/MMmm,/ Fig. 35. Section reduced to half natural scale, of the vegetable mould m a field drained and reclaimed 15 years before. Showing turf, vegetable mould without stones, mould with fragments of burnt marl, coal cinders and quartz pebbles; and subsoil of black peaty sand with quartz pebbles. After Darwin. 148. Soil Removal.âPitted against these processes of growth there is a powerful and universal set of agencies con- stantly operating everywhere to transport from higher to lower levels and from the land to the sea the surface soils, and the magnitude of this action has been estimated at not far from one foot each 3,000 years as an average for the whole land surface, and hence the saperficial and exhausted soils are being slowly removed and replaced by new soil originating from the products of rock decay, and brought to the surface by capillary action and that of burrowing animals generally. The absolute amount of soil removal can be appreciated when it is understood that the summits of the bluffs represented in Figs. 36 and 37 show the general level of the surrounding lower land at a former time and that, at times intervening
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishermadis, bookyear1894
