As you noted, per Wikipedia, “Mintmarks appear underneath the tail feathers of the bald eagle on the reverse between the letters D and O in Dollar.”

If you really do have an 1895 Philly dollar, it might be worth talking to a reputable, long-standing local coin dealer, who can possibly help you send to one of the ‘big’ coin certification services (PCGS, NCG, ANACS) so that they can verify it as genuine and assign a grade (condition). You can also do the research about how to send the coin directly to one of these services.

Detailed info about those coin grading services:

Doing so may cost $50 or so, but if the coin is worth as much as is suggested in this guide, it may be worth it. You’d probably want to send it, or have a dealer send it, via Registered Mail.

You could also consider talking to one of the larger US coin dealers/auction houses, even if they’re not local. It might help if you can take and post (to a private space to which you can provide guest access on Flickr, Photobucket, etc.) some high resolution photos of the coin, so these dealers can look at it and give you a preliminary assessment. Some names you might look for in a Yahoo! or Google search:

Heritage, Superior, Goldberg, ANR, Stack’s, Bowers & Merena

If it’s an 1895 proof, which are without a mint mark, it could be quite rare (although the listing says that some had their mint marks removed by fakers).

I’d take it to a reputable coin dealer for an appraisal. Of course, the value would depend upon its condition (being in a field makes me think that it’s not in very good condition).

Good luck! I hope that you have something really unusual!