It consists of an accumulation of cracked and scorched stones that were used to heat water in a communal cooking trough .
A kidney - shaped burnt mound located near Castle Geo in the south - east of Stroma can be more confidently ascribed to prehistory .
Stroma consists of an accumulation of cracked and scorched stones that were used to heat water in a communal cooking trough .
A kidney - shaped burnt mound located near Castle Geo in the south - east of Stroma can be more confidently ascribed to prehistory .