 The rise in population during the 12th and 13th centuries created a need for increased agricultural output, and trees were cleared in the forests (assarting) and marsh reclaimed for use as arable land.Agricultural efficiency also improved during this period with, for example, the practice of applying a clay and lime mixture termed marl as a fertiliser from the early 13th century, earlier than in much of Britain.Marl pits were common in some parts of the county.