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Show '302 DENUDATION OF 'rilE LAND. CrrAP. Vl ca.rrieJ further down the valley. Closely si1nilar results, with respect to the thickness of the mould, were obtained in a neighLourino· valley. St. Catherine's I-Iill, near Winchester, is 3 27 feet in height, and consists of a steep cone of chalk about i of a mile in diameter. The upper part was converted by the Roman , or, as smne think, by the ancient Britons, into an encampment, by the excavation of a deep and broad ditch all round it. Most of the chalk removed during the work was thrown upwards, by .which a projecting bank was formed ; and this effectually prevents wormcastings (which are numerous in parts), stones, and other objects from being washed or rolled into the ditch. The mould on the upper and fortified part of the hill was found to be in most places only from 2! to 3i inches in thickness; whereas it had accumulated at tho foot of the embankment above the ditch to a thickness in most places of from 8 to 9 ~ inches. On the embankment itselfthe mould was only 1 to 1! inch in thickness ; and within the ditch at the bottom it varied from 2! to 3 ~' but was in one spot 6 inches in CrrAP. VI. MOULD OVER TilE CllALK. 303 thickness. On tho north-west side of the hill, either no embankment had ever been thrown up above the ditch, or it had subsequently been removed ; so that here there was nothing to prevent worm-castings, earth and stones being washed into the ditch, at the bottmn of which the mould formed a layer from 11 to 22 inches in thickness. It should however be stated that here and on other parts of the slope, the bed of mould often contained fragments of chalk and flint which had obviously rolled down at different times from above. The interstices in the underlying fragmentary chalk were also filled up with mould. My son examined the surface of this hill to its base in a south-west direction. Beneath the great ditch, where the slope was about 24°, the mould was very thin, namely, from li to 2~ inches; whilst near the base, where the slope was only 3° to 4°, it increased to between 8 and 9 inches in thickness. We may therefore conclude that on this artificially modified hill, as well as in the natural valleys of the neighbouring Chalk Downs, some fine earth, probably derived in large part from |
