The title to a book I read...

[bolverk]

In junior high I read a book about a group of kids who were caught in a cave-in in an old mine. A group of bullies was chasing another group, they all went in the mine, and boom. The book tells of them trying to survive. The only other two events I can clearly remember are them almost being rescued by searchers in an ground opening above them - but no dice - and them finding glowing moss to light their way. I also don't think the book had a happy ending. I think the book ends with them either dying or still lost in the dark. Maybe set in the British isles. Anyone?