地壳稳定，外营力作用于起伏的地表，使其削高填洼逐渐变为平面，形成准平原。随后地壳抬升，准平原受切割破坏，残留在山顶或山坡上的准平原，称为夷平面。如果山地曾发生多次间歇性上升，将会形成若干个分布在不同高度的夷平面，这种多层地形是判断区域间歇性升降运动的重要标志。

When the crust is stable, under the effect of external geologic agent, the rolling surface of the earth gradually become the peneplain. With the uplift of the crust, the peneplain is cut and damaged, those which are left on the top of the mountain or on the hillside, are known as the planation surface. If the mountain has experienced several intermittent uplifts, several planation surfaces will be formed at different heights. This multilayered terrain is an important sign to judge regional intermittent uplift and drop movement.