By means of T-S area diagrams, a method of analysis is developed for the study of closely spaced hydrographic data. In a transitional zone, such as that over the continental shelf off southern New England, this method is useful for following the continuity of the mixing process. Changes in salinity at the edge of the shelf are due, for the most part, to horizontal advection. There are indications of nonisentropic mixing on a smaller scale. From the turbulent features of the region, as indicated by instabilities, this condition is not unexpected.