We found these rocks in Ontario, Canada a number of years ago and have no idea how they might have formed nor have we seen any even remotely similar. They look like someone stood around slowly dripping wet cement on the ground and let them harden, which I suppose is what they very well could be, but on some of them both the top and bottom have the same pattern so I don't think its possible that they could have formed that way. But I don't claim to know a great deal about rocks.
Any help would be awesome! These things have been stumping us for too long.