The name "Tembeling Formation" is introduced for fluviatile-deltaiclacustrine sediments of post-orogenic origin in West Malaysia (Malaya). A type section is described in the Tekai River (Pahang), where the total thickness of the formation is over 3,000 meters. The age of the formation is probably late Triassic to Jurassic. A basal member, the "Murau Conglomerate", is described from the Mersing area (Johore); it consists of coarse red purple polymict conglomerates of fluviatile origin. These conglomerates decrease in thickness from east to west and vary in composition. The Murau Conglomerate is overlain in the Tahan Range by a sequence of red to grey shales and mudstones alternating with thick bands of arenaceous-rudaceous rocks. The top of the formation is formed by typical argillaceous red-beds, deposited under warm continental conditions. The Tembeling Formation overlies rocks of varied composition and age. An angular unconformity well developed in the east of the Peninsula decreases in importance westward. Along the east coast in the State of J ohore, the formation unconformably overlies metasediments of probable Carboniferous age, whereas to the northwest in the type area in central Pahang Triassic rocks are underlying. The folded Tembeling Formation is unconformably overlain by flat-lying beds of the late Jurassic to early Cretaceous Gagau Group.