Northern Europe is comprised of large islands and peninsulas, including the British Isles and Scandinavian Peninsula. The region has rough, rocky hills and low mountains, with more fertile farmland and plains found in southern parts. Glaciers have left their mark through coastal features like fjords and lakes. Natural resources from water, forests, soils, and energy sources have made Northern Europe wealthy, including oil and gas reserves in the North Sea, hydroelectric and geothermal energy, timber forests, and fertile land for agriculture. Despite seeming cold, the climate is actually mild due to warm ocean currents, bringing marine west coast climates to areas like Denmark, Britain, and western Norway.