This paper presents four terrain diagrams, on a scale of 1:1,000,000, which cover all the Philippine Islands. The diagrams were prepared during World War II by the Military Geology Unit of the U. S. Geological Survey for the Chief of Engineers, U. S. Army. Terrain features shown on the diagrams owe their individuality to the nature of the rock formations and the tectonics. Mountain areas are made up of pre-Tertiary basement rocks, and of Tertiary and Quaternary volcanics; Tertiary and Quaternary sediments from the lowland areas. The mountain areas of basement rocks are geanticlines or horsts, and the lowland areas of Tertiary sedimentary rocks are downwarps. A striking tectonic feature, which has strongly influenced the terrain, is the Philippine fault zone, a belt of dislocation which extends southeast from Luzon to Mindanao.

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