Many stones were, until quite recently, whitewashed. A few still are. Most people think that this is a folk-memory of libations with milk. However, in a male dominated world the alternative is just as likely.
If the search facility was available I could dig out several threads about the possibilites of groups of priests 'emptying their sacks' over the stones in an offering to Mother Earth. Afterall, it ain't milk that fertilizes is it?