When the temperature of the ocean changes with depth within a horizontal layer, it is accompanied by a change in the velocity of sound. The reflection of sound from such a transition layer depends on the incident angle and wavelength of the sound, the thickness of the layer, the manner in which the velocity changes, and the total amount of the change. The usual formula for reflection assumes a transition layer of negligible thickness. The reflection coefficient then depends only on the incident angle and the total velocity change. This case is treated and numerical values are given for the reflection coefficient under conditions of practical interest. It is then shown that for a gradual velocity change which corresponds to certain temperature data, the reflection coefficient for small glancing angles of incidence changes gradually with increasing layer thickness and may be approximated very closely by the usual formula. Quantitative comparison of the cases is made and the general applicability of the approximation is discussed.