The Republic of Colombia is situated in the northwest corner of South America, bordering on the Caribbean Sea on the north and on the Pacific Ocean on the west. The western half of the country includes a portion of the Andes where this mountain system becomes divided into several ranges, while the eastern half includes the vast piedmont plains known as the llanos, which stretch monotonously eastward o t the Orinoco, there to merge with the western margins of the Guayana Shield. Thus topography and geology of the republic are varied and in some places of great complexity. Some areas are still very imperfectly known, and there are naturally many controversial questions in structural, regional, and stratigraphic geology. In this general review it is aimed to avoid a discussion of these questions as much as possible, although in some instances it is necessary to make a definite choice. The opinions expressed herein are those held by the majority of the Committee on Colombia.
For the release of much data on Colombian geology the author is deeply indebted to the Tropical Oil Company of Bogotá; also to Dr. D. Trumpy, former Chief Geologist for the Compania de Petroleo Shell de Colombia and to Dr. W. Hatfield, Chief Geologist for the Texas Petroleum Co. at Bogotá. The portion of the paper dealing with igneous and metamorphic rocks was contributed by the Shell Company, and that on structure was prepared by Dr. Hatfield.
The history of serious geologic studies in Colombia commenced