Examination of peat cores and pollen records indicates that soil erosion (suggesting clearance of woodland for agricultural purposes) was taking place in 3470 BC (the early Neolithic era); much later, from 2460 BC, evidence of arable cultivation exists. As the climate became damper, peat expanded its coverage at the expense of woodland, and post-glacial sea level changes left raised beaches around the coastline 18–45 metres above the present sea-level, especially between Harris and A'Bhrideanach; Bronze Age artefacts, such as barbed-and-tanged arrowheads typical of the Beaker People, have been found in the machair which replaced it.