The Sedimentation Unit and Its Use in Field Sampling'

Four objectives of quantitative study of sediments are outlined, each of which requires specially collected samples. The corresponding techniques of collection are here called engineering sampling, descriptive sampling, environmental sampling, and correlation sampling, according to the purpose of the samples. The steps in the systematic collection of samples for the first three purposes are outlined. Certain principle~ • nderlying efficient correlation sampling are considered. There are two techniques for environmental sampling depending on the kind of measurements to be made. Criteria are given for determining whether or not composite samples may be used. When composite samples are unsuitable, samples from individual layers are required. In the latter case, the sedimentation-unit concept furnishes a practical field tool for the rational selection of the layer or combination of layers to be sampled as a unit. An example of the use of the sedimentation unit , showing how the boundaries of the individual units are determined, is given in detail. Six general steps for the determination of a sedimentation unit are given. Devices for obtaining the samples are described.