Portal de Periódicos da CAPES

The Nature and Origin of the Soils over the Cornish Serpentine

1956; Wiley; Volume: 44; Issue: 2 Linguagem: Inglês

10.2307/2256839

1365-2745

D. E. Coombe, L. C. Frost, Michael Le Bas, W. A. Watters,

Plant Ecology and Soil Science

The principal types of heath community found upon serpentine rock on the Lizard peninsula, Cornwall, England, and some of the features, so far as they affect plant growth, of the correlated soils have been described by Coombe and Frost (1956). In their paper little consideration was given to the soils as pedological entities nor was it considered whether the heath types, each with its characteristic soil, can be ranged either in a developmental series in time or a vegetation-soil catena in space (cf. Milne, 1935; Morison et al., 1948; Balme, 1953). Before going further it is necessary to examine the assumptions that the parent material of the soils which occur over the serpentine is (i) uniform, and (ii) is in fact the serpentine itself, assumptions which are basic to any hypothesis of a developmental series of soils and which would affect the interpretation of any physiographic complexes of vegetation and soil. Flett (1946) assumes more than once that the serpentine weathers to give at least some of the soils upon it. For example: 'On the surface of the Lizard platform there are practically no deposits except the products of the decomposition of the subjacent rocks. As this part of England was never covered by moving ice-sheets there is a complete absence of material transported from a distance by glacial action' (loc. cit., p. 5). 'The unmodified serpentine of the downs yields a yellow or buff clay full of weathered blocks; this soil is shallow and the bare rock projects or is everywhere near the surface. The ferruginous clay is almost impermeable to water and after heavy rains the surface of the downs is covered with water which slowly drains away. In a few places the serpentine is decomposed or disintegrated to a depth of several feet, but the soil is sterile' (loc. cit., p. 174). The 'ferruginous clay' is probably the soil of 'Tall Heath' (Erica vagans-Schoenus heath) and the sterile, deeper soil that of 'Short Heath' (Agrostis setacea heath). Coombe and Frost also assumed at first that the soils were derived from the serpentine, since areas were deliberately avoided where concealed intrusions of other rocks (e.g. the granite-gneisses), or recognized thin deposits of sedimentary material (e.g. the Pliocene Crousa gravels), or windblown shell sand (e.g. near Kennack Sands) clearly contributed to the parent material. Since the areas selected for study have never been cultivated (at least within historic times) or enclosed, the complications due to the carting and spreading as fertilizer of shell sand or rotted hornblende schist or granite-gneiss do not arise. However, the interpretation of the series of soils of increasing depth and acidity from 'Rock Heath' (Festuca ovina-Calluna heath) through 'Mixed Heath' (Erica vagans-Ulex europaeus heath) to 'Short Heath' (Agrostis setacea heath) as a simple