Airplanes for carrying on geological investigations in difficultly accessible regions is recommended, and the practicability of this method of exploration is discussed. The problem of keeping a geologic party that has been transported by airplane also equipped and supplied by the same means of transportation and the utility of the airplane for reconnaissance by a geologist and for photographic purposes are treated. A considerable part of the paper is devoted to a description of the types of land and sea planes now in use by the United States Army Air Service and the Navy Bureau of Aeronautics that are serviceable for geological investigations in more or less remote regions. The amphibian in most cases will doubtless be the most serviceable and economical as well as the sa est type of plane for an oil or mining company to use in such work. It is reasonable to predict that it will be a relatively short time before a two-motor amphibian plane will be perfected and such a plane will be extremely servicable for geological expeditions into remote regions.