peninsulas: Kopli, Paljassaare, and Kakumäe Peninsulas. The city has a number of public beaches, including those at Pirita, Stroomi, Kakumäe, Harku, and Pikakari. The geology under the city of Tallinn is made up of rocks and sediments of different composition and age. Youngest are the Quaternary deposits. The materials of these deposits are till, varved clay, sand, gravel, and pebbles that are of glacial, marine and lacustrine origin. Some of the Quaternary deposits are valuable as they constitute aquifers, or as in the case of gravels and sands, are used as construction materials. The Quaternary deposits are the fill of valleys that are now buried. The buried valleys of Tallinn are carved into older rock likely by ancient rivers to be later modified by glaciers. While the valley fill is made up of Quaternary sediments the valleys themselves originated from erosion that took place before the Quaternary. The substrate into which the buried valleys were carved is made up of hard sedimentary rock of Ediacaran, Cambrian and Ordovician age. Only the upper layer of Ordovician rocks protrudes from the cover of younger deposits, cropping out in the Baltic Klint at the coast and at a few places inland. The Ordovician rocks are made up from top to bottom of a thick layer of limestone and marlstone, then a first layer of argillite followed by first layer of sandstone and siltstone and then another layer of argillite also followed by sandstone and siltstone. In other places of the city, hard sedimentary rock is only to be found beneath Quaternary sediments at depths reaching as much as 120 m below sea level. Underlying the sedimentary rock are the rocks of the Fennoscandian Craton including gneisses and other metamorphic rocks with volcanic rock protoliths and rapakivi granites. These rocks are much older than the rest (Paleoproterozoic age) and do not crop out anywhere in Estonia. Climate Tallinn has a humid continental climate (Köppen climate classification Dfb) with mild, rainy summers and cold, snowy winters. Winters are cold, but mild for its latitude, owing to its coastal location. The average temperature in February, the coldest month, is . During the winters, temperatures tend to hover close to freezing, but mild spells of weather can push temperatures above , occasionally reaching above while cold air masses can push temperatures below an average of 6 days a year. Snowfall is common during the winters, which are