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Show 258 DISINTEGRATION, ETC. CnAr. V. "hundred yards." * Nor should we forget, in considering the power which worms exert in triturating particles of rock, that there is good evidence that on each of acre of land, which is sufficiently damp and not too sandy, gravelly or rocky for worms to inhabit, a weight of more t11an ten tons of earth annually passes throurrh their. bodies and is brought to the b surface. The result for a country of the size of Great Britain, within a period not very long in a geological sense, such as a million years, cannot be insignificant; for the ten tons of earth has to be multiplied first by the above number of years, and then by the number of acres fully stocked with worms; and in England, together with Scotland, the land which is cultivated and is well fitted for these animals, has been estimated at above 32 million acres. The product is 320 million n1illion tons of earth. * Anniversary Address: 'The Quarterly Journal of the Geological Soc.' May 1880, p. 59. ( 259 ) CHAPTER VI. 'l'HFJ DENUDA'l'ION OF 'l'IIE LAND-continued. D~nu~ation aided by recently cjecte1l cas tioga !lowing llown mchned grass-covered surfaces-The amount of earth which an~ually ~ows ~?wn wards-The ellcct of tropical rain on wotm castmgs-lhc finest particles of earth wa~:~l 1 ed com~ Iotel! away from castings-'l'ho disintegration of dried cast.-I? gs wto p~llets, and their rolling down inclined surfaces' Ihe form~t10n of little ledges on hill-sides, in part duo to tho accumulatiOn of disintecor ratod castinoo- s - Cast·m gs bl own to leeward over lovol land-An attempt to estimate the amount thus ~lown-'l'he degradation of ancient encampments and tun~uh-The preservation of the crowns and furrowl:l on land anciently ploughed-Tho formation and amonnt of mould over the Chalk formation. WE are now prepared to consider the more direct part which worms take in the denuda~ tio~ of the land. When reflecting on subaenal denudation, it formerly appeared to me, as it has to others, that a nearly level or very gently inclined surface, covered with turf, could. suffer no loss during even a long lapse of time. It may, however, be urged that at long intervals, debacles of rain or s 2 |