We tend to think of water in terms of a particular purpose: is the quality of the water good enough for the use we want to make of it? Water is fit for our own use but may be unfit for another's. We may, for instance, trust the quality of lake water enough to swim in it, but not enough to dri...

The exposed rock that you see along the Mississippi River is mainly sedimentary. The events that formed the area surrounding the Mississippi river tell a story about what has been there before. The igneous rocks present at the surface and under the surface near the site of the Mississippi River were...