The old ferry crossings were later to develop into the busy river quays of the eighteenth and nineteenth centuries. In mediaeval times the transport of goods to supply the Benedictine abbey at Tavistock, four miles by track from the river port of Morwellham, was significant. Sea sand from the coast was imported to spread on farmland, until in the eighteenth century a dressing of lime was found to be more beneficial. Large quantities of limestone and coal were then imported to burn in the numerous limekilns on the river quays; the lime had to be made locally as it was not slaked before application and was too reactive for transport by water after burning. Later, street sweepings and other refuse from Plymouth and Devonport, together with bones for the newly discovered bone fertiliser, were carried inland to manure the fields. Other regular imports were timber from British Columbia and the Baltic, in large baulks for use as supports in the mines, and coal from Wales to supply the mine pumping engines.