thanks Moss. there are a couple of legends associated with the Cona Bhacain. one is that it was used as a stake by Fingal around which to tie Bran, because the nearby fort was believed to be Fingal's home. there are a series of these forts dotted around Glen Lyon at strategic entry points to the glen, and one legend has it that they were all the homes of Fingal and his warriors

the other legend is a fertility one - if girls crawled under the protruding part of the stone then they wouldn't become pregnant

more here http://www.stravaiging.com/history/ancient/site.php?id=134

Cheers
Andy