what kind of stones are those?
They are local stones from Northern Minnesota. I only know about them because I'm a white water kayaker and they are from a small rock island between two class 3/4 rapids. The island is only accessible when the water is low a few months of the year because you must climb down a 20 foot ledge/waterfall and cross the rapids to get at it. It's inaccessible by kayak because the rapids are too swift. I'm going to do a two week ph test on them starting tonight to see how they affect water quality. They've already passed the vinegar test.