Silt three grades fine, medium and coarse 0.002 mm to 0.006 mm to 0.020 mm to 0.063 mm). In actuality, silt is chemically distinct from clay, and unlike clay, grains of silt are approximately the same size in all dimensions; furthermore, their size ranges overlap. Clays are formed from thin plate-shaped particles held together by electrostatic forces, so present a cohesion. Pure silts are not cohesive. According to the U.S. Department of Agriculture Soil Texture Classification system, the sand–silt distinction is made at the 0.05 mm particle size. The USDA system has been adopted by the Food and Agriculture Organization (FAO).
Ardleigh Gravel Pit Ardleigh Gravel Pit Ardleigh Gravel Pit is a 1.2 hectare geological Site of Special Scientific Interest south of Ardleigh in Essex. It is a Geological Conservation Review site. The site exposes a succession of Pleistocene levels, with an interglacial between two glacial periods. The interglacial may date back 700,000 years. The site has plant microfossils rare or unique in Britain, and according to Natural England's description in 1992, it may become the type site for a previously unrecognised British early middle Pleistocene interglacial. The site is divided into two areas. The main one is L-shaped, forming the sloping south-east and