Complex sentence: The excavators employed former quarry workers (the last Tintagel cliff quarry was closed in 1937), who worked under a trained foreman and who were instructed to clear the land on the Island, following and exposing any walling that they came across and keeping any finds.
Split into simpler sentences: The excavators employed former quarry workers (the last Tintagel cliff quarry was closed in 1937) who worked under a trained foreman. They were instructed to clear the land on the Island, following and exposing any walling that they came across and keeping any finds.