But sound is a product of an oscillation that provokes the molecules of the medium (atmosphere) to move up and down.
Sound waves in air are longitudinal waves. They compress and expand the air in the direction of propagation of the wave. The molecules don't go up and down, but forward and backward. You can have similar waves in water and their speed has the same property as the speed of sound in air. You can have variations in the propagation speed when the space through which the sound propagates gets very narrow, but in typical conditions, there is negligible dispersion.
The other answers provide information about the surface waves, which are longitudinal waves.