Geologists attached to European colonial administrations began many years ago the study of the geological structures and succession of strata in all other Southeast Asian countries. In Thailand, little work was undertaken before 1930. Actually, the only geological observations of Thailand proper before that time were those made by Högbom in 1912 in the course of a four months visit to many parts of Thailand, and those made by W. Lee, while he was in the employ of the Royal Thai State Railways Administration in 1921-1922 in Northern Thailand and the Peninsula.
Geological field work in Thailand is hampered by the very thick cover of weathering products and weathered rocks which almost everywhere obscures the parent materials, by the dense tropical vegetation, by the lack of road and railway cuts in many parts of the Kingdom, and by the general absence of mines and quarries. Nevertheless, a start was made in the 1930's when the Thai Government Department of Mines obtained the services of some young Western-trained geologists.
In 1949 and 1950 the United States Geological Survey sent a party of geologists to Thailand. Their studies, made in cooperation with the Thai geologists, resulted in an excellent geological report, 4 from which much of the following information is taken.