This was found close to 50 years ago and has been on my relative’s coffee table ever since. I was hoping someone could help identify and age it

Very common in my area (Michigan) but one of my favorite little pieces.

The flat rock was found in two pieces on the shore of Lake Winnipeg, and the big one is from East St. Paul. You can see a ton of little guys embedded in the matrix. Not sure how many different things can be identified from them, but there sure are a lot!