The monument includes the well preserved standing remains of two lead ore hearth smeltmills and the buried remains of a third. The first smeltmill at Marrick was built by John Sayer in 1574-5. Built near the site of the later Low Mill, it is thought to have been the first in Swaledale, and one of the earliest nationally. By 1660 a second mill (High Mill) was built 50 metres uphill and to the west of the first. It is thought that Sayers mill closed before 1705. Low Mill was extensively rebuilt in the 1830s by Jaques and Company, and renovated in 1862 by the Hurst Mining Company who installed a circa 6 metre diameter waterwheel. High Mill had been declared beyond repair in 1861 and was incorporated into the flue system from Low Mill. Smelting finally ceased after the mines reverted to selling ore to independent smeltmills in 1868. The monument includes the well preserved ruins of the 19th century Low Mill which stands to eaves height and retains a pair of intact furnace arches. Attached to the north wall are the ruined remains of a slag hearth building which contains the remains of the slag hearth which is thought to have been installed in the 1862 renovation. To the south of the bellows chamber are the ruined remains of the wheelpit. Approximately 12 metres to the west of the slag hearth building are a pair of stone built bingsteads with flagged stone floors. Stone footings of the original 16th century smeltmill have been identified lying underneath the smeltmill complex. The remains of a double flue extends from the north west corner of the smeltmill. It is thought that High Mill was converted into a condensing chamber in 1861. High Mill is believed to date to the 17th century. Like Low Mill it is also well preserved with a pair on intact furnace arches. Scheduled.