Silt semi-arid environments that substantial quantities of silt are produced. Silt is sometimes known as "rock flour" or "stone dust", especially when produced by glacial action. Mineralogically, silt is composed mainly of quartz and feldspar. Sedimentary rock composed mainly of silt is known as siltstone. Liquefaction created by a strong earthquake is silt suspended in water that is hydrodynamically forced up from below ground level. In the Udden–Wentworth scale (due to Krumbein), silt particles range between 0.0039 and 0.0625 mm, larger than clay but smaller than sand particles. ISO 14688 grades silts between 0.002 mm and 0.063 mm (sub-divided up into
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