What is an artesian well?

In an artesian well, the water leaps into the air like a geyser from under the earth. Sometimes a layer of porous rock or sand is buried between two layers of solid rock which water cannot permeate. At some point the porous layer is exposed to the surface. Water from rain or snow sinks downward and is trapped between the watertight layers above and below. When released by digging an opening, water gushes out forcefully.