Alison - It's my understanding that there were/are many linen mills in the Belfast area. Belfast Linen was famous the world over.

For a hilarious song with a reference to Belfast Linen check out "The Ballad of William Bloat" in the DT data base. I first heard it sung before a live audience by the Clancy Bros. -- it's the only song I've ever heard that ends with three consecutive "punch lines", each getting a bigger laugh from the audience than the one before!