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The Subis Limestone complex is situated about 60 miles south of Miri and just north of the Niah river in Sarawak, Northwest Borneo.The complex is of triangular shape with side lengths of approximately 3 miles. The maximum measured thickness of limestone is about lo00 feet. These limestones form vertical escarpments and have a strongly developed karstic surface. Caverns are very common, the largest being the Niah Cave.The complex is situated on the culmination of a northeast-southwest trending anticline that is reverse faulted along the fold axis. The southeastern partdips towards the southeast while the northwestern part gently dips to the northwest.The age of the complex is TeS (Lower Miocene) as evidenced by the combined occurrence of Edepidina sp and Miogysina sp. Shales of the Setap Formation deposited contemporaneously with the limestones belong to the Gtobigerim binaiensis zone (combined occurrence of Globigednddes trilobus/immafurus group and G. binaienris)). also of Lower Miocene age.The Subis complex is an isolated carbonate development underlain, surrounded and covered by ciastic sediments. It apparently formed on a palhigh resulting from slight tectonic uplift. The wast at that time was nearby and located to the south or southwest.Lower Miocene (Tq limestones are found in several other places in Northwest Borneo: in the Suai wells to the west, the upper part of the Melinau Iimestone sequence to the east and the Gomantong limestones in Sabah.