therefore not meaningful. The majority of the population live in areas with a Mediterranean climate (southern Europe), a temperate maritime climate (western Europe), or a warm summer continental or hemiboreal climate (in eastern member states). Geology Europe's most significant feature is the dichotomy between highland and mountainous Southern Europe and a vast, partially underwater, northern plain ranging from the British Isles in the west to Poland in the east. These two halves are separated by the mountain chains of Pyrenees, Alps, Carpathian and Balkan Mountains. The northern plains are delimited in the west by the Scandinavian mountains. Major shallow water bodies submerging parts of the northern plains are the Celtic Sea, the North Sea, the Baltic Sea complex, and the Barents Sea. The northern plain contains the old geological continent of Baltica, and so may be regarded as the "main continent", while peripheral highlands and mountainous regions in south and west constitute fragments from various other geological continents. The geology of Europe is hugely varied and complex, and gives rise to the wide variety of landscapes found across the continent, like the rolling plains of Hungary. Climate The climate of the European Union is of a temperate, continental nature, with a maritime climate prevailing on the western coasts and a mediterranean climate in the south. The climate is strongly conditioned by the Gulf Stream, which warms the western region to levels unattainable at similar latitudes on other continents. Western Europe is oceanic, while eastern Europe is continental and dry. Four seasons occur in western Europe, while southern Europe experiences a wet season and a dry season. Southern Europe is hot and dry during the summer months. The heaviest precipitation occurs downwind of water bodies due to the prevailing westerlies, with higher amounts also seen in the Alps. Tornadoes occur within Europe, but tend to be weak. The Netherlands experiences a disproportionately high number of tornadic events. The mildest climate within the European Union occurs in the Portuguese island of Madeira, where the average temperature varies from during the day and at night in winter to during the day and at night in summer. Also, the mildest climate occurs in the Spanish island of Gran Canaria (Canary Islands), where the average temperature varies from during the day and at night in winter to during the day and at night in summer. Both these islands lie in the Atlantic. As for the