I found this on the beach off Lake Ontario

[alfredgeorge]

This reacts to a magnet and my metal detecter. It appears to have rust on it. I hope someone can tell what it is.

 

[Mud Hut]

coprolite?

 

[AU Seeker]

I believe that it's a bit of iron slag, the Great Lakes are littered with slag of all types from the numerous smelters/iron works that dotted the shore lines.

 

[Terry Soloman]

Wow! You found a "Leaverite!"