I agree with Nhbenz about the "Great Seal of the United States" rosette. Here's a photo of one with the attachment bar intact on its back.
The other item has been reported to be a US Army horsegear trace-chain swivel link. Some sellers on e-Bay claim it is civil war era, but I believe that is incorrect, it is from the late-1800s to World War One era... like the rosette you found at the same dig-site.
Regarding your trace chain swivel link, CBG is right, it's not civil war. I have one just like it off of army surplus harness that we were using in 1964 or 65, so it probably dates to WWI or a bit later, perhaps closer to WWII, because the harness was still useable at the time.