varying between in the morning to in the afternoon at coastal areas. Miri has the lowest average temperatures in comparison to other major towns in Sarawak and has the longest daylight hours (more than six hours a day), while other areas receive sunshine for five to six hours a day. Humidity is usually high, exceeding 68 per cent, with annual rainfall varying between and for up to 220 days a year. At highland areas, the temperature can vary from to during the day and as low as during the night. Sarawak is divided into three ecoregions. The coastal region is rather low-lying and flat with large areas of swamp and other wet environments. Beaches in Sarawak include Pasir Panjang and Damai beaches in Kuching, Tanjung Batu beach in Bintulu, and Tanjung Lobang and Hawaii beaches in Miri. Hilly terrain accounts for much of the inhabited land and is where most of the cities and towns are found. The ports of Kuching and Sibu are built some distance from the coast on rivers while Bintulu and Miri are close to the coastline where the hills stretch right to the South China Sea. The third region is the mountainous region along the SarawakKalimantan border, where a number of villages such as Bario, Ba'kelalan, and Usun Apau Plieran are located. A number of rivers flow through Sarawak, with the Sarawak River being the main river flowing through Kuching. The Rajang River is the longest river in Malaysia, measuring including its tributary, Balleh River. To the north, the Baram, Limbang and Trusan Rivers drain into the Brunei Bay. Sarawak can be divided into two geological zones: the Sunda Shield, which extends southwest from the Batang Lupar River (near Sri Aman) and forms the southern tip of Sarawak, and the geosyncline region, which extends northeast to the Batang Lupar River, forming the central and northern regions of Sarawak. The oldest rock type in southern Sarawak is schist formed during the Carboniferous and Lower Permian times, while the youngest igneous rock in this region, andesite, can be found at Sematan. Geological formation of the central and northern regions started during the late Cretaceous period. Other types of stone that can be found in central and northern Sarawak are shale, sandstone, and chert. The Miri Division in eastern Sarawak is the region of Neogene strata containing organic rich rock formations which are the prolific oil and gas