The November/December 2008 issue of Archaeology magazine contains an article titled “Witches of Cornwall,” about odd, ritualistic or votive burials of skins, eggs, and other items at a place called Saveock Water.

These burials took place from the 1640s at least through the 1950s.

There is as yet no link to the article (so ask a librarian), but this site gives some of the same information.

The writer, Kate Ravilious, creates a purely hypothetical spell that might have accompanied one of the offerings:

Take a swan and wring its neck. Skin the bird and, under a full moon, lay its skin in a shallow hole with the feathers face-up. Add eggs–five for every child you want to bear. Atop each egg, place the talon of a blackbird and a black stone. Circle the hole three times, clockwise, then close it with a clod of earth. As soon as you are with child, empty the hole, or terrible things will come to pass.

(Wringing the neck of an angry adult swan might be harder than Ms. Ravilious realizes, however. Apparently her magic is not for the faint-hearted.)

UPDATE: Archaeology put a link up.