mainly of two forest massives: Harmaakallo and Bosmalm. The most famous and most popular nature area in Espoo is the Nuuksio National Park located on the lake highland of northern Espoo, reaching over to Kirkkonummi and Vihti. As well as the contiguous forest and pools of sweet water, Nuuksio contains small bogs and meadows. There are also lush grove-like brook valleys in the area. The highest spot in Espoo, Mustankorvenkallio, is located in Velskola to the southwest of Saarijärvi 114 metres above sea level and over 40 metres above the water level of Saarijärvi. There are also considerably high spots very near the coast, such as the Kasavuori hill in Soukka, rising to 44 metres above sea level. Inland waters There are over a hundred lakes and ponds in Espoo, of which 73 have an area of over a hectare. The lakes in Espoo were formed when the land slowly started rising after the continental ice sheet had thawed, and water started flowing into the crevices in the bedrock. The oldest lakes in Espoo are Kalatoin, Iso Majaslampi, Orajärvi and Pieni Majaslampi, all located over 80 metres above sea level. At that time, what is now the Baltic Sea was in a so-called Yoldia Sea phase, which had formed when the surface of the Baltic Ice Lake had lowered tens of metres in a short time. Nuuksio slowly expanded into part of the mainland and new lakes were formed when the sea level sank. Development stopped for about a millennium and a half when the ancient Baltic Sea changed into the Ancylus Lake. Its surface was originally about 60 metres above the current sea level. The Ancylus Lake formed into the salty Littorina Sea when the current Danish straits started opening up. The surface of the Littorina Sea was about 34 metres above the current sea level. At that time, almost all lakes in northern Espoo had been separated from the sea. Only the lake Nuuksion Pitkäjärvi remained as a narrow, fjord-like bay. The shore of the Littorina Sea remained at its place for a long time as upthrust slowed down. Rocky rims remain of the ancient sea shore on hills and cliffs. Nuuksion Pitkäjärvi only separated from the sea and became an inland lake about five millennia ago. About four millennia ago the land had risen so far that also Lake Bodom, Lippajärvi and other pools in central Espoo