Science Buddies: "Ask an Expert"

I placed a small amount of rock salt in the bottom of a glass and covered it with about four ounces of tap water. In a few days the glass is covered with salt above the water line. Why does this happen?

My guess would be the following:

1) some salt dissolved in the water (perhaps not all of it)
2) some of the water evaporated, lowering the water level
3) some of the formerly dissolved salt stuck to the side of the glass; as the water level went down, it "came out of solution" (lost contact with the water)

I can go into further detail if needed, but I would recommend going into the Physical Science subforum for Experts who are more tuned to chemistry. Also please note that this forum is for discussing science fair projects - it would help us if you could frame the question in the context if your project in the future!