That particular style of cast eagle two-piece buckle, was quite popular in the decade leading up to the Civil War. Currently, I'm working on compiling information on the various varieties of two-piece "tongue-and-wreath" buckles, that were in use during the 1840's and 1850's. Eventually, I will be putting together a book covering these types of buckles. There are many styles, and designs, that were not covered in the works of O'Donnell & Campbell, and Kerksis.
The cast eagle buckle, (like your example), had a plain cast wreath, with a gutter back. There are several different varieties, (and sizes) of that particular cast eagle buckle. Yours is the more common style, (not that I'm saying that any are a real common find), of the several varieties with slight differences. The majority of the known excavated examples of these particular cast eagle buckles, have come from Western U.S. sites. My research points to the possibility that many of these could have actually been made in the West during the 1850's. I have included some photo examples of similar buckles for your reference.
Congratulations on a nice find! Now go find the cast wreath!
CC Hunter
[attachment 36332 CastEagleO.jpg][attachment 36345 CastEagle2.jpg]
[attachment 36343 CrudeEagleO.jpg]
[attachment 36346 CastBucklesO1.JPG]
[attachment 36341 CC-Buckles2.jpg]