Studies in the post-glacial history of British vegetation. XI. Late-glacial deposits in Cornwall

Abstract

In a series of profiles at the china-clay pits at Hawks Tor, Bodmin Moor, Cornwall, a stratigraphy was found resembling that typical of the late-Glacial Allerod oscillation. Gravelly-soil layers showing solifluction phenomena overlie the organic muds and peats of a small channel, and these gravels are in turn thickly overlaid with peat. Pollen-analyses from this site, reinforced by series from neighbouring sites, make it clear that the peat above the solifluction gravel must be referred to the early post-Glacial period. Identification of fruits, seeds, etc., from the organic layers near the overlying and underlying gravels shows the presence of many plants now restricted to more northerly parts of the country, such as Betula nana, Salix herbacea and Thalictrum alpinum . Pollen-analyses show assemblages of genera and species of herbaceous plants recognized as typical of the open ‘tundra’ or ‘park-tundra’ conditions found elsewhere in Europe in this period; these include the genera Helianthemum, Armeria, Artemisia, Thalictrum, Planlago and Polemonium . Evidence that the muds and peats beneath the upper gravel layer were formed in a period of amelioration is found in the formation of the organic layers themselves, in the diatom flora, which has a preponderantly cool-temperate character, and in the presence of a few mosses and phanerogams of more southerly distribution type. The evidence does not make it apparent whether closed woodland characterized this period. There seems no doubt that these deposits represent the late-Glacial period, and the authors make a tentative zonal correlation between them and zoned deposits of similar age elsewhere in Britain and other parts of north-west Europe, extending through the Allerod oscillation. The lists of microscopic and macroscopic plant identifications from the recognized zones provide evidence of the presence of a large number of plant species at a time and place of great interest and importance in the history of the British flora.