A beautiful place, shame about the barbed wire fencing that criss crosses across the hill...covered with the remains of neolithic minings and 19ct mining evidence. Follow the sheep trails (I always use animal tracks) for the best walk. Many interesting *natural* features make this hill worthy of your time!
Probably the source of Holy McGrail's folklore, this is from Hunt's 1886 'Popular Romances of the West of England'.
At Ransom Mine the "Knockers" were always very active in their subterranean operations. In every part of the mine their "knockings" were heard, but most especially were they busy in one particular "end." There was a general impression that great wealth must exist at this part of the "lode." Yet, notwithstanding the inducements of very high "tribute" were held out to the miners, no pair of men could be found brave enough to venture on the ground of the "Bockles." An old man and his son, called Trenwith, who lived near Bosprenis, went out one midsummer eve, about midnight, and watched until they saw the "Smae People" bringing up the shining ore. It is said they were possessed of some secret by which they could communicate with the fairy people. Be this as it may, they told the little miners that they would save them all the trouble of breaking down the ore, that they would bring "to grass" for them, one-tenth of the "richest stuff," and leave it properly dressed, if they would quietly give them up this end. An agreement of some kind was come to. The old man and his son took the "pitch," and in a short time realised much wealth. The old man never failed to keep to his bargain, and leave the tenth of the ore for his friends. He died. The son was avaricious and selfish. He sought to cheat the Knockers, but he ruined himself by so doing. The "lode" failed; nothing answered with him; disappointed, he took to drink, squandered all the money his father had made, and died a beggar.
(Rosewall Hill mines were also known as Ransom United Mine)(http://www.mindat.org/loc-1261.html)
According to "Myths & Legends of Cornwall" (C.Weatherhill & P.Devereux), the mines on Rosewall Hill were haunted by Knockers (weird sprite-like things). A miner called Trenwith formed a partnership with the Knockers, and benefitted from their expertise at mining ore. Trenwith would leave 1/10th of properly dressed ore as payment to the Knockers. This relationship continued after Trenwith's death via his son, who one day sought to cheat the Knockers. The lode then failed, he became a drunk who lost all his father's money and ended up a beggar.
Sounds like a lovely metaphor for earth-lights, respect for the land and other weirdness to me.