Details

The monument includes a large earthfast slab of granite with at least 17
circular or oval shaped hollows, here argued to have been ore-grinding
mortars, worn into its upper face. The site lies within the 'Cornwall and
West Devon Mining Landscape' World Heritage Site, site No. 17. The mortar
outcrop is situated on the northern edge of the floodplain associated with
the River Cober.

The hollows are similar to those found on mortar stones associated with tin
stamping mills, but their disposition precludes mechanical formation. The
hollows vary considerably in size and depth with the largest one being 22cm
long by 20cm wide and 10cm deep. The interior of all the hollows are worn
smooth as a result of the crushing process. The hollows are all situated
along the southern part of the outcrop and were formed by hand crushing of
tin ore from the nearby alluvial streamwork. Hand crushing of ore is
considered to have been carried out in Cornwall before stamping machinery was
introduced during the medieval period. Using field evidence alone the
precise dating of this tin ore crushing site is not possible. It would,
however, fit most comfortably into the later prehistoric period when
particularly rich ore recovered from the adjacent streamwork could have been
economically crushed by hand.

The modern barrier erected to prevent vehicles straying onto the monument is
excluded from the scheduling, but the ground beneath is included.

MAP EXTRACT
The site of the monument is shown on the attached map extract.

Source: Historic England

Reasons for Scheduling

The mortar outcrop at Trenear, 9m north east of Poldark Mine entrance is the
only known example of an early hand tin-crushing site in the South West of
England. The outcrop survives very well because it has until recently been
protected by a layer of soil, which may also preserve rich environmental and
archaeological information; particularly in the area adjacent to the southern
edge of the rock.

Source: Historic England

Sources

Other
Fieldwork by S. Gerrard, Gerrard, S., (2004)

Source: Historic England