In the old abbey gardens at Tresco is a curious stone, about four feet long, two feet wide, and six inches in thickness, in an upright position. Near the top are two holes, one above the other (one being somewhat larger than the other), through which a man might pass his hand. It is supposed to be an old Druidical betrothal or wishing-stone, and used before the monks built the abbey at Tresco. Young people, engaged to be married, would pass their hands through the holes, and, joining them together, would so plight their troth. As a wishing-stone, or to break a spell, a ring woudl be passed through the holes with some incantations. – J.C. Tonkin’s Guide to the Isles of Scilly.
p40 in
Cornish Folk-Lore
M. A. Courtney
The Folk-Lore Journal, Vol. 5, No. 1. (1887), pp. 14-61.