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Show 288 DENUDATION OF THE LAND. CHAP. VI. six observations made at a di tance of 10 yards outside the embankment. The thickness of the mould within two of the circular trenches was measured every 5 yards all round, on the inner sides near the bottom. My son Horace protracted these measurements on paper; and though the curved line representing the thickness of the mould was extremely irregular, yet in both diagrams it could be seen to be thicker on the north-eastern side than elsewhere. When a mean of all the measurements in both the trenches was laid down and the line smoothed, it was obvious that the mould was thickest in the quarter of the circle between north-west and north-east; and thinnest in the quarter between south-east and southwest, especially at this latter point. Besides the foregoing measurements, six others were taken near together in one of the circular trenches, on the north-east side; and the mould here had a mean thickness of 2·29 inches; while the mean of six other measurements on the south-west side was only 1·46 inches. These observations indicate that the castings had been blown by the south-~est winds from the circular enclosed space mto CrrAP. VI. CASTINGS BLOWN TO LEEWARD. 289 the trench on the north-east side ; but many more measurements in other analogous case would be requisite for a trustworthy result. The amount of fine earth brought to the surface under the form of castings, and afterward~ transported by the winds accompanied by rain, or that which flows and rolls down an inclined surface, no doubt is small in the course of a few scores of years; for otherwi ·e all the inequalities in our pasture fields would be smoothed within a much short.er period than appears to be the case. But the amount which is thus transported in the course of thousands of years cannot fail to be considerable and deserves atten6on. E. de Beaumont looks at the vegetable mould which everywhere covers the land as a fixed line from which the amount of denudation may' be measured.* l-Ie ignores the contiuued formation of fresh mould by the disintegration of the underlying rocks and fragments of rock; and it is curious to find how much more philosophical were the views, main- * 'Le9ons de Geologie pratique, 1845; cioquieme Leyon.' All Elie de Beaumont's arguments are admirably controvcr!Nl by Prof. A. Geildc in his essay in Transact. Geolog. Soc. of Glasgow, vol. iii. p. 153, 1868. u |