I recently found this scythestone in an extremely rural vintage store in Wallowa county Oregon. I immediately jumped to believing it was a Pike hone from Pike (Haverhill) New Hampshire. My further research hasn't contradicted that. (Or provided any conclusive evidence.) So this might be Bethlehem gneiss from the Issac > Alonzo Pike quarry. The founding product for Pike Manufacturing.
Any additional information about or images of Pike scythestones would be appreciated. I have a book coming on interlibrary loan.