Well, I've mostly passed old marbles by, not knowing enough to know what is what. However, I happened to give these old clay ones (plus one large one made of wood)  a close look at a recent flea market, and I must say they completely captivated me with their beauty; I am converted!

I believe these date to the mid-to-late 19th century, and I believe several of them, with shiny salt glazes, are "Benningtons", which were made in Germany. (They are identifiable by both their coloring and the little “eyes” that they have, from where they were touching during firing. That gorgeous rose pink one near the top and the brown one below in the first image are two, and I've learned the pinks are in fact pretty rare.)

I'd just put these in a beautiful bowl to admire and pick up now and then. The set includes 16 clay and 1 wood marble and what I believe it a pretty old fabric pouch in which they came. (I'll string a thin ribbon through it as a cinch closure before mailing.) The largest ones (shooters) measure about 3/4" in diameter, the smallest 1/2" d.  All in very good condition.