Clay. The Upper Greensand was also once known as either the "Malm" or "Malm Rock Of Western Sussex" Both Upper and Lower Greensand outcrops appear in the scarp slopes surrounding the London Basin and the Weald. Prominent seams are to be found in the Vale of White Horse, in Bedfordshire, in Kent, Surrey, the South Downs National Park, elsewhere in Hampshire, the Isle of Wight, and the Jurassic Coast in Dorset. The soil of the greensand is quite varied, ranging from fertile to fairly sterile. On the fertile soils chestnut and stands of hazel and oak are common, while Scots pine and birch colonise the poorer soils. These Greensand Ridges are popular long distance walking routes, for instance the Greensand Way in Kent. Lower Greensand The Lower Greensand (known as the Woburn Sand north of the London Basin) is of Aptian age. In the Weald the Lower Greensand consists of four deposits which are partly diachronous: the Atherfield Clay thick, the Folkestone Beds thick; the Hythe beds thick and the Sandgate Beds thick. Although it appears both north and south of the London Basin it is not present everywhere beneath the Chalk Group which underlies the basin; the Gault lies directly on eroded Jurassic or Devonian rocks under much of the area. Upper Greensand The Upper Greensand is of Albian age. It represents a sandy lithofacies deposited in areas of stronger currents than the Gault Clay. Like the Lower Greensand it is not present beneath the whole of the London Basin, apparently passing laterally into Gault clay east of a line between Dunstable and Tatsfield and of uncertain extent to the east of London. Outcrops of the Upper Greensand occur in the southwest of England including the Blackdown Hills and East Devon Plateau and the Haldon Hills, remnants of a once much wider extent. Properties and uses The green color of greensand is due to variable amounts of the mineral glauconite, an iron potassium silicate with very low weathering resistance; as a result, greensand tends to be weak and friable. It is a common ingredient as a source of potassium in organic gardening and farming fertilisers. Greensand glauconite is used as a water softener for its chemical-exchange properties. Greensand coated with manganese oxide (called manganese greensand) is used in well water treatment systems to remove dissolved (reduced) iron and manganese with the addition of an oxidant, usually potassium permanganate, under