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Show 142 AMOUNT OF EARTH CnAP. IlL certainly more than forty years before, a large hole had been filled up with coarse red clay, flints, fragments of chalk, and gravel ; and here the fine vegetable mould was only from 4 t to 43 inches in thickness. In another and undisturbed place, the 1noulJ varied much in thickness, namely, from 6 ~ to 8~ inches; beneath which a few small fragments of brick were found in oue place. From these several cases, it would appear that during the last 29 years mould has been heaped on the surface at an average annual rate of from ·2 to ·22 of au inch. But in this district when a ploughed field is first laid down in grass, the mould accutnulates at a much slower rate. Tlw rate, also, must become very much slower after a bed of 1nould, several inches in thickness has been fonned ; for the worms then live ' chiefly .near the surface, an l bun ow down to a greater depth so ns to bring up fresh earth from below, only during the winter when the weather is very cold (at which time worms were found in this fielJ at a depth of 26 inches) and during summer, when the weather is very dry. CrrAP. III. BHOUGll'l' UP BY WORMS. 143 ~ field, which adjoins the one just desc~ Ibed, slopes in one part rather steeply (viz., at from lOo to 15o); this part was last ploughed in 1841, was then harrowed and left to become pasture-land. For several years i~ was clothed with an extremely scant vegetatwn, and was so thickly covered with small and large flints (some of them half as large as a child's head) that the field was always cal1ed by my sons "the stony field." When they ran down the slope the stones clattered together. I remember doubting whether I ~hould live to see these larger flints covered With vegetable mould and turf. But the smaller stones disappeared before many years had elapsed, as did every one of the larger ones after a time; so that after thirty years (1871) a horse could gallop over the compact turf from one end of the field to thri other, and not strike a single stone with hit shoes. To anyone who remembered the appearance of the :field in 1842, the transformation was wonderful. This was certainly the work of the worms, for though castings were not frequent for several years, yet. some were thrown up month after month, and |
