I just cleaned the gutters of the house we bought last year, and there
was ~1" of a sandy dirty debris in the bottom of the gutters. It
looked like some dirt mixed with the sandy/pebbly offal from the
roof's shingles.

I'm thinking this might be very good to add to the composting bin, or
very bad. Anyone have experience doing this, or know if this stuff
might contain something that would be harmful either to the bacteria
breaking down the compost or to the vegetable garden once we add it
there?