The Action of Colloids in Precipitating Fine-Grained Sediments

With certain well-known exceptions, ancient sandy and clayey sediments do little more than approach a condition of uniform grain-size. The so-called clays, silts and sands, and their consolidated equivalents, the mudstones, shales, silt-stones and sandstones, receive their appellation in most cases from the dominant grade present. Actually they consist of a mixture of particles, distributed over a considerable range of grain-size, in which the dominant grade, especially in the case of the finer deposits, often amounts to less than 50 per cent of the whole.