Grain size and grain size distribution
Sediments can be separated from each other by grain-size. A sample collected from a deposit is sieved through sieves of different mesh widths. Below is a typical grain size distribution of till, material deposited by a glacier, and glaciofluvial sediments, material deposited by a meltwater river, by percentage on each of the sieves.
Grains finer than 0.063 mm are called clay (finest particles) and silt, grains from 0.063 mm to 2mm sand, grains from 2 mm to 6.4 cm pebble, grain from 6.4 cm to 25.6 cm cobble and grains coarser than 25.6 cm boulder. See also this website.