Thanks. That's cool. Meshes with and fleshes out my general impressions. "Agate" types. Yes, I know that vocabulary. Good distinction from the Onyx types.
LOL. Anyway, here are pix of a possibly 1932-ish package containing feathered slags together with tweeners, i.e., "marbles which some call rainbos and some say look like they might be from the NLR era" . . *inhale deeply*.