The RCAHMS database says that this stone is 1.45m tall, 1.25m wide, and up to 0.6m thick at the base. Just downhill from the stone, if you follow the stream it stands by (the Peatshiel Sike), near a waterfall is the Brownies Cave (so, fair enough, this story is not connected to the stone, but something nearby..). The brownie used to help out at the local farm. But it might not be worth looking for him.
The brownie of the farm-house of Bodsbeck, in Ettrick, left his employment upwards of a century ago [..]. He had exerted himself so much in the farm - labour both in and out of doors, that Bodsbeck became the most prosperous farm in the district. He always took his meat as it pleased him, usually in very moderate quantities and of the most humble description. During a time of very hard labour, perhaps harvest, when a little better fare than ordinary might have been judged acceptable, the goodman took the liberty of leaving out a mess of bread and milk, thinking it but fair that at a time when some improvement, both in quantity and quality, was made upon the fare of the human servants, the useful brownie should obtain a share in the blessing. he, however, found his error, for the result was, that the brownie left the house for ever, exclaiming,
'Ca', brownie, ca',
A' the luck o' Bodsbeck away to Leithenha'.'
The luck of Bodsbeck accordingly departed with its brownie, and settled in the neighbouring farm-house, called Leithenhall, whither the brownie transferred his friendship and services.
p108 of Select Writings of Robert Chambers By Robert Chambers (1847).