Interval velocity v in relatively pure clastic sediments can be expressed as a function of depth z by the formula v = v o (1 + cz/v o4 ), where v 0 is a constant characteristic of the rock and c = 3.3 km 3 /sec 4 , approximately. From this relation can be deduced a function v 4 = 9.5cz, which prescribes the minimum velocity possible at a given depth and the maximum depth at which a given velocity can occur. An upper limit of velocity is set by data from limestones and from refraction measurements at depths from 8 to 50 km. The limiting curves converge near 150 km depth toward a function v 5 = 180z, which holds from 200 km to the boundary of the core at 2900 km. The relation of near-surface velocity to porosity is discussed, and it is shown how one can deduce the motion of shorelines during deposition.