We collected a few fossils from out in the East Lothian area a year or so ago. There was once a tropical sea bed which stretched over most of Scotland. Fossils aren't everyday finds for us, but they show up in rivers all over the country.
Scotland was a tropical paradise once. Some sources indicate the fossils here are about 330 million years old. There's no way to tell, of course, since sea creatures didn't keep records.
These are a mix of crinoids, Burrows from some kind of worm, and one of them looks like it has a shrimp. I daresay it's not a shrimp, but at first glance you'd see a mini shrimp.
I put some in the tumbler experimentally. They went stage 1 and 2, then I tried to skip to final polish because limestone doesn't tumble well. They don't have much shine at all. If you have 1000 grit sandpaper and some free time you could finish it off perfectly. I like them as they are. You can really see the shapes of the Corals.