Liquids that don't mix, also known as immiscible liquids, will form layers when they have different densities. The denser liquid will sink to the bottom, while the less dense liquid will float on top.

Here's why this happens:

* Density: Density is a measure of how much mass is packed into a given volume. A denser liquid has more mass in the same amount of space.

* Gravity: Gravity pulls everything downwards. The denser liquid, with its higher mass, is pulled down more strongly, causing it to sink below the less dense liquid.

Examples:

* Oil and water: Oil is less dense than water, so it floats on top.

* Mercury and water: Mercury is much denser than water and will sink to the bottom.

* Vinegar and olive oil: Vinegar is denser than olive oil.

Let me know if you'd like to explore any specific immiscible liquids in more detail!