shaped, hilly, and . Because it was once part of continental South America, Trinidad has an assortment of tropical vegetation and wildlife considerably more varied than that of most Caribbean islands. Tobago has a generally similar but less varied assortment. Geology Geologically, the islands are not part of the Lesser Antilles Volcanic Arc. Rather, Trinidad was once part of the South American mainland and is situated on its continental shelf, and Tobago is part of a sunken island arc chain related to the Pacific-derived Caribbean Plate. The islands are separated from the continent of South America by the Gulf of Paria; Bocas del Dragón, a -wide northern passage; and Serpent's Mouth, a -wide southern passage. The Northern Range consists mainly of Upper Jurassic and Cretaceous metamorphic rocks. The Northern Lowlands (East–West Corridor and Caroni Plains) consist of younger shallow marine clastic sediments. South of this, the Central Range fold and thrust belt consists of Cretaceous and Eocene sedimentary rocks, with Miocene formations along the southern and eastern flanks. The Naparima Plains and the Nariva Swamp form the southern shoulder of this uplift. The Southern Lowlands consist of Miocene and Pliocene sands, clays, and gravels. These overlie oil and natural gas deposits, especially north of the Los Bajos Fault. The Southern Range forms the third anticlinal uplift. It consists of several chains of hills, most famous being the Trinity Hills. The rocks consist of sandstones, shales, siltstones and clays formed in the Miocene and uplifted in the Pleistocene. Oil sands and mud volcanoes are especially common in this area. Political geography Trinidad is split into 14 regional corporations and municipalities, consisting of 9 regions and 5 municipalities, which have a limited level of autonomy. The various councils are made up of a mixture of elected and appointed members. Elections are due to be held every three years with the last elections held in 2019. The island of Tobago is administered by the Tobago House of Assembly. Climate The country lies in the tropics, enjoying a generally pleasant maritime tropical climate influenced by the northeast trade winds. In Trinidad the annual mean temperature is , and the average maximum temperature is . The highest temperature ever was 37.8 degrees Celsius. The lowest (coldest felt) temperature recorded in Trinidad was in January 1964. The humidity is high, particularly during the rainy season, when it averages 85 to 87%. The island receives an average