In order to effect a state of stratified flow in which the source of interfacial turbulence would be the instability of the interface itself, apparatus was devised which would permit the counter flow of two superposed streams of different densities to be maintained for a considerable period of time over an appreciable length of uniform passage. By means of chronophotography of injected droplets and analysis of point samples of fluid, measurements were made of velocity and density distributions across the interface for various flow regimes. In accordance with indications of dimensional and stability analyses, results were presented in the form of dimensionless ratios of interfacial shear and of mass transport as functions of the Froude and Reynolds numbers.