Cailleach Bheur (pronounced ‘cal’yach vare’) is rumoured to haunt Schiehallion, and other mountains like Ben Nevis.
She is a frightening blue-faced hag – a personification of Winter, and also called ‘the daughter of Grianan (the winter sun)’. The Cailleach was reborn each All Hallows and went about smiting the earth and calling down snow! On May Eve she threw down her staff under one of her wintery plants, the holly or the gorse, and – interestingly – turned into a grey stone for the summer. One wonders how many standing stones were therefore associated with her. In another version she turns into a beautiful girl at the end of winter.
She also looks after various animals – deer (which she herds and milks, and protects from hunters), swine, wild goats and wolves. She was also known as a guardian of wells and streams.
As Katherine Briggs says in her ‘Dictionary of Fairies’, a whole book might be written about her and her variants. She seems widespread as well – there is another blue-faced supernatural woman in Leicestershire: Black Annis.
Insa Thierling has an article on the Cailleach at caerclud.vscotland.org.uk/cailleach.html
She mentions that there is a Sgrìob na Caillich, or Cailleach’s Furrow on Schiehallion. It is where she has been with her plough, causing furrowed patterns in the rocks – a scree? There is one on Jura too.