In Darkest Africa Value?

Obscured in my bookshelf, I recently discovered a 2 volume set of Henry Stanley's In Darkest Africa (Illustrated w/ maps). I believe them to be the first American edition, for they were published in 1890, not so long after the book itself was originally published elsewhere. It's in fine condition, the spine loose, though quite unnoticable, and the interior is not worn to any extent. So, based on the description given, what would the value of this edition be estimated at (in $)?