Unified Soil Classification System group symbol. For example, GW-GM corresponds to "well-graded gravel "with silt"." If the soil has more than 15% by weight retained on a #4 sieve (R > 15%), there is a significant amount of gravel, and the suffix "with gravel" may be added to the group name, but the group symbol does not change. For example, SP-SM could refer to "poorly graded SAND with silt" or "poorly graded SAND with silt and gravel." Unified Soil Classification System The Unified Soil Classification System (USCS) is a soil classification system used in engineering and geology to describe the texture and grain size
Fern House Gravel Pit no public access. Fern House Gravel Pit Fern House Gravel Pit is a 1.3 hectare geological Site of Special Scientific Interest in Fern, near Bourne End in Buckinghamshire. It is also a Geological Conservation Review site. This site exposes the Pleistocene Taplow Gravel formation, and may help to elucidate a poorly understood period in the history of the River Thames, between glacial Anglian stage, around 450,000 years ago, when the river was diverted south to its present course, and the warm Ipswichian around 120,000 years ago. Fossils found at the site include straight-tusked elephants and mammoths. The site is on