Graeme C's 'Yorkshire Rock Art' site has this quotation:
WELL OF THE CUPS, North Uist. PSAS vol 16 p 400. - Near the old churchyard on the Ardivoran peninsula, there is a holy well called the Well of the Cups. The spring of water flows from beneath a rock which has a cross carved on it, there are also several cup marks along the top of the rock and on other stones nearby. An old inhabitant remembered hearing that people used to make an Easter pilgrimage to the holy well, taking hard boiled pashe eggs with them to place in the cup marks around the well.
According to the Scottish Monuments Record on Canmap, the well was variously known as the well 'of the priest', 'of the cross' and 'of the cups'. Above it is a massive rock and just above the high water line, a 14" Latin cross has been inscribed.
Nine yards to the SE are 24 cupmarks arranged along the twin narrow and parallel ridges of a boulder embedded in the beach. Other cupmarks are said to exist, both above the well and on various stones at the NE side of the same promontory, but perhaps some of these are natural hollows.