Archaeological Discoveries in the Raised Bogs of the Somerset Levels, England

Abstract

When C. E. Moss (1907) first described the vegetation of the peat areas of the Somerset Levels, he referred to them as ‘moors’, a term offering no distinction from upland peats such as those of the Pennines or Dartmoor. It was not until much later that they were recognized as the remnants, much degraded and dissected by peat-cutting, of an extensive complex of raised bogs (Godwin 1941). This was a conclusion of considerable significance since raised bogs belong to the category of ombrogenous mires, that is to say, of peat structures built up in almost total dependence on rain and snow falling directly upon them, and drawing not at all upon ground water. Such bogs receive very little mineral supply and become very acidic and poor in plant nutrients, so that their vegetation is highly specialized and most characteristic, consisting very largely of species of the moss genus Sphagnum, various flowering plants of the order Ericales, cotton-grass, deer-grass (Trichophorum caespitosum) and a restricted number of other species of equally restricted range. It is the various assemblages of the remains of these plants that allow us to identify given peat samples as having formed in raised bog, and often permit us to relate them to given communities characteristic of different aspects of the vegetation of still-active raised bogs.This is a very helpful circumstance, since the raised bogs are entities in such close dependence upon annual precipitation that they respond quickly to phases of increased or decreased wetness by altered surface vegetation. Thus in periods of dryness they become covered with ling (Calluna vulgaris), cotton-grass (Eriophorum vaginatum) and sometimes trees, chiefly birch (Betula verrucosa), and the peat then formed is very colloidal, dark and fully humified. By contrast, when it is continuously wet the bog surface is covered with actively-growing Sphagna (which form a matrix for the associated higher plants), and the peat formed in these conditions is pale, fibrous, and undecayed. An abrupt transition from the one peat type to the other, if consistent across a bog, is referred to as a recurrence-surface (RY is the familiar contraction from the Swedish word).