I agree with Steph that there is a very good chance that agate is German. The way I check for hand-faceting is to shine a bright light on the marble and look at the small reflection it makes, i.e., the little dot of bright light on the surface of the marble. Then rotate the marble slowly and see if the that little bright spot jumps around or moves smoothly across the surface of the mib. The light spot will appear to wiggle around if the marble is hand-faceted. For comparison, you can do the same using a machine-made glass marble and you will see how the reflection moves smoothly if there are no facets.