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Show 296 DENUDATION OF TilE LAND. CrrAP. VI. observed. In a fourth case, the mould in a furrow in the upper part of a sloping field was 2! inches, and in the lower part 4! inches in thickness. On the Chalk Downs at about a mile dis-tance from Stonehenge, my son William exa. Inined a grass-covered, furrowed surface, sloping at from 8° to 10°, which an old shepherd said had not been ploughed within the 1nemory of man. The depth of one furrow was measured at 16 points in a length of ti8 paces, and was found to be deeper where the slope was greatest and where less earth would naturally tend to accumulate, and at the base it almost ds appeared. The thickness of the mould in this furrow in the upper part was 2! inches, which increased to 5 inches a little above the steepest part of the slope; and at the base, in the middle of the narrow valley, at a point which the furrow if continued would have struck, it amounted to 7 inches. On the opposite side of the valley, there were very faint, almost obliterated, traces of furrows. Another analogous but not. so decided a case was observed at a few 1niles distance from Stonehenge. On the CHAP, VI. MOULD OVER TilE CIIALK. 297 whole it appears that the crowns and furrows on land formerly ploughed, but now covered with grass, tend slowly to disappear when t~e surface is inclined; and this js probably 1n large part due to the action of worms; but that the crowns and furrows last for a very long time when the surface is nearly level. Formation and amount of mould over the Chalk Formation.-W orm-casting·s are often ejected in extraordinary numbers on steep, grass-covered slopes, where the Chalk comes close to the surface, as my son William observed near Winchester and elsewhere. If such castings are largely washed away during heavy rains, it is difficult to understand at first how any mould can still remain on our Downs, as there does not appear any evident means for supplying the loss. There is, moreover, another cause of loss, namely, in the percolation of the finer particles of earth into the fissures in the chalk and into the chalk itself. These considerations led me to doubt for a time whether I had not exaggerated the amount of fine earth which flows or rolls down grasscovered slopes under the form of cast in o-s · and b ' |