WITH regard to the laws governing the transport, sorting, and deposition of sediments, much has still to be learned, but one fact emerges clearly from the mass of present data. During the process of transport by water the load undergoes selective treatment, or, in other words, is sorted. The late Dr. G. K. Gilbert, in the course of his important work on the transportation of débris by running water, carried out experiments with mixtures of several grades of detrital material and found that before the slope of the stream had been definitely established (i.e. before the attainment of uniformity of conditions), and especially when low velocities were used, the current tended to sort the débris, building deposits with the coarser part and continuing to transport the finer material. This fact has a special bearing on the study of natural sediments. The state of equilibrium, or of perfect uniformity of conditions, is seldom, if ever, completely realized in nature, and even when approximately reached is not, as a rule, of long duration.