The purpose of this report is to present all available published data bearing on the rate of increase of underground temperature with increasing depth in the United States, together with several hundred original observations by myself and my associates. A canvass of the governmental, State, and serial publications has yielded many records of temperature of flowing wells and also a few observations made with thermometers in borings and deep mines. Additional data on temperature of flows have been given by correspondents. Some of the data, especially those relating to flows from wells, may not be reliable, and as a rule these could not be discriminated. Many records are omitted because no facts are available as to the source of flow.
