Railroad question, when i was a kid early 60s we used to find these large clear round marbles?

Question

they were around the tracks, what are they and do they still use them, my boys and i walked were walking down the tracks in the middle of the desert and we found 1 and a german made tally counter, way out in the desert on some tracks while we were exploring,, thanks to all that answer

Answer 1

Glass. In an unrefined state.

I used to find iron pellets.

The Rat