What final story did Edgar read to Roderick?

From the text:

"The antique volume which I had taken up was the "Mad Trist" of Sir Launcelot Canning; but I had called it a favourite of Usher's more in sad jest than in earnest; for, in truth, there is little in its uncouth and unimaginative prolixity which could have had interest for the lofty and spiritual ideality of my friend. It was, however, the only book immediately at hand....."