strike it rich,
Hope you were not offended by the horsing around.
Square nails such as those were common in the latter half of the 1800s around here (Eastern U.S.). Another important thing to remember is that a LOT of things were recycled back in the "old" days, so it's possible to find those in more recent structures.
When out in the boonies, nails were a very precious commondity! Although a "dime a dozen" today, some detectorists don't realize how valuable nails used to be!
Good luck with your site,
Cavers5