Clouds around 7,000 and 24,000 feet are considered mid-level clouds, and they are composed of mixtures of water and ice. Clouds above 20,000 feet are generally considered high-level clouds. These are the highest that clouds can go, and these are generally very wispy and long, made of ice. Fog forms when water vapor condenses on the ground. It is basically water vapor that moves close to solid areas.
Stratus clouds are very gray and long and they usually resemble fog in the sky.
They are very weak in terms of rain, because of their fog-like nature, but they can sometimes cause moisture and brief condensation to fall. They form when vertical air currents lift a thin layer of air to a point where condensation is possible. Cirrus clouds are the thin clouds that usually stretch from west to east across a sky. They resemble a beard, and many ancients thought they were the hair of deities in the sky. These clouds always form above 18,000 feet, and are non-rain in nature.