There are several "Union Brewing" companies listed in the "Tavern Trove" website. You might be able to narrow it down to a location based on where it was dug. The loop seal closure dates it to the time frame Andy gave. Nice logo.
Most of the Union Brewery bottles from Michigan are pretty similar with a slug plate and no picture. There is a Michigan Union Brewing Co. from Ann Arbor which depicts an eagle w/ shield.
I got a rare Union bottle from Adrian Michigan, not listed in the American Breweries book. Looks different then yours. The Ann Arbor bottle is common depending on what variation it is. Theres a Union in the U.P. also. Not sure where yours is from. Pic of mine below.
Great info! Does the eagle look like the Anheuser/Budweiser eagle to you? If it is, I'm wondering if it's a local brewery somewhere that was an agent for Anheuser. I'm asking about this bottle for someone else and I don't know where in Michigan it was dug, or if it's even a Michigan bottle. But that's all we have to go on. Again, Thanks everyone and keep the ideas coming.
EDIT- Bottle was found in an excavation in Trenton, Michigan, just south of Detroit.
You might be thinking of the post which has the eagle & shield with the W, which ended up being Wiedemann Brewing. The eagle was represented for too many breweries to list. For anyone looking at beer bottles, Bruce has an excellent website called Beer Bottle Library. Type those 3 word and you will find a great resource for cataloged blob and blown beers listed by State and City. RC