During the Quarternary period, the climate fluctuated between cold and warm periods known as ice ages and interglacial stages. During the ice ages the sea level was very low. Glaciers appeared in the Scandinavian highland, later spreading to the surrounding lowlands including Denmark. During the interglacial stages, the ice disappeared and the distribution of land and sea was similar to today. Traces of four ice ages and three interglacial stages have been found in Denmark, along with signs of the period which followed the last ice age. This postglacial period incorporates the present day. The only thing known about the first ice age, known as the Menapian period, is that Denmark was covered by ice. The only evidence of the Cromerian interglacial stage which followed the Menapian comes from a small number of lake sediments. No marine sediments have been found from this period. The Elsterian ice age, which followed, was an important ice age during which the ice sheet extended as far as Central Europe. Traces of three different glacial advances have been found in Denmark. At the end of the Elsterian period, and during the subsequent Holsteinian interglacial stage, parts of the south of Jutland and the Limfjord area were covered by the sea. Little is known about the land area during the Holsteinian interglacial stage, since the only remnants that have been found are a small number of lake sediments. During the subsequent Saalian ice age, the ice sheet again reached Central Europe. Signs of another three glacial advances have been found in Denmark dating back to this period. The Saalian period left its mark on the landscape in West Jutland in the form of the so-called "hill islands" surrounded by melt water plains from the last ice age, the Weichselian period. The northernmost part of Jutland was covered by the sea right from the end of the Saalian period, throughout the Eemian interglacial stage and during the first part of the Weichselian ice age. The southern part of Denmark, on the other hand, was only submerged during the Eemian period. A number of lake deposits have been found dating back to this period, one of which contains traces of the people who lived in the area at that time. During the Weichselian period, the last ice age, Denmark was a tundra plain which was repeatedly invaded by glaciers. The main glacial event was an ice advance towards the main line of ice stagnation in Jutland; it was while the ice stood here that the melt water plains around the hill islands were formed. The glaciers then advanced to the ice margin in the east of Jutland. Glacial deposits on the Danish islands were left during the following period and bear witness to the presence of a number of terminal moraines. It was these events during the Weichselian period which resulted in the formation of the Danish ice age landscape. Towards the end of the Weichselian period, the northernmost part of Jutland was covered by the sea. Subsequent uplift then introduced the so-called "Continental period" which lasted into the first part of the subsequent postglacial period that began some 10,000 years ago. By then, the ice had melted away in the south of Scandinavia and the forests were beginning to move into Denmark. The country was much larger during the Continental period than it is now; the land stretched as far as England. The Continental period was followed by the Flandrian transgression during the Stone Age, when vast areas of land were submerged as a result of a rapid rise in sea level. This was followed by an uplift of the northern part of Denmark, exposing large areas of the sea floor. The present coastline began to take shape.