problems of geology?" feeling assured that ultimately all such research will be of economic value.

In the first decade of the Survey's existence its geologic work was largely devoted to the investigation of the broad problems of American geology, and the formulation of a fundamental geologic classification as the scientific basis for the preparation of the geologic map of the United States. As the major features of this basic problem approached solution, the Survey's attention was increasingly turned to the geological survey of the country. Researches in geologic history and theory have nevertheless been steadily prosecuted. Thus, for some time past the Survey has been engaged in a study of the work of glaciers, the geologic history of the continent during the Quaternary period, and the classification and correlation of the sedimentary rocks of the entire country, work involving the study of all North American fossil faunas and floras and their comparison with those of other parts of the world.

Broad geologic research may involve correlative research in physics and chemistry. Among the researches of this type carried on by the Survey are those relating to questions of terrestrial physics, such as the mechanics of the Panama Canal slides, the variation in the water content of rocks from Panama, the increase of earth temperatures with increase of depth, and the electric activity of ore deposits.

In addition to chemical and physical researches directly related to geologic researches, the Survey from time to time has made researches which may be said to be directed to the elucidation of general physical and chemical problems that have no exclusive relation to the development of geologic theory. Thus, work has been done by the Survey in a revision of the fundamental atomic weights, on the radio-activity of ores, and on the geochemical interpretation of water analyses. Much of the work now done by the Carnegie Geophysical Laboratory was begun in the Geological Survey.

Compilation of Information Relative to Mineral Deposits and the Mineral Industries. In addition to its activities in connection with the exploration of mineral deposits, the Survey collects, compiles and disseminates information relative to all known mineral deposits in the United States, and relative to the production of minerals.

The circumstances under which the Survey began in 1882 its publication of the annual report on the "Mineral Resources of the United States" are set forth in the preceding chapter. In 1905 authority was obtained from Congress (act of March 2, 1905, 28 Stat. L., 960) to publish the separate parts or chapters of this report in pamphlet form as soon as they were transmitted to the printer, it being provided that "the report of the Mineral Resources of the United States shall

be * * * printed for each preceding calendar year as soon as compiled and transmitted for publication, and that the separate chapters on any given mineral product, such as iron, coal, building stone, and so forth, shall be printed as rapidly as transmitted for publication." This act was passed only to insure prompt publication. "Advance chapters" had been issued long before this act was passed.

In early years, the work of the Survey in this field was confined largely to the compilation of statistics of production. More recently the tendency has been to emphasize the importance of data relative to the occurrence, technology and utilization of the mineral resources of the country. Simultaneously the effort has been to publish more promptly the statistics of production, and at present weekly, monthly and quarterly statistics regarding certain mineral products are being collected.

The collection of statistics showing the production of minerals in the United States involves a complete annual canvass of all the mineral producers, a complete list of whom is kept by the Survey. This canvass is made largely by correspondence, but is supplemented by field work. The technical press is also carefully scrutinized for new names. As a further

means of keeping the lists of producers up to date, the lists are printed every year and distributed to persons familiar with the industries for corrections and additions.

In the preparation of its statistical reports for the last six years, the Survey has worked in coöperation with a number of the state geological surveys, the statistics thus collected being used jointly by the state and federal surveys. This coöperative agreement avoids annoyance to the producers by duplicate requests for statistical information and insures more prompt and more complete returns. Eighteen state surveys are now coöperating in this way.

"Mineral Resources of the United States," which for several years has consisted of two volumes, is still the chief medium through which information concerning the country's mineral industries is made public. In addition to this annual compilation and the more frequent shorter periodical statistical statements given largely through the press, the Survey publishes from time to time a report on a particular mineral or group of minerals from material obtained in the course of its investigations. A type of these special compilations is a volume. published in 1917, entitled, "Useful Minerals of the United States," giving the location, by states and counties, of the principal deposits of useful minerals, and a glossary showing the composition and character of each mineral, the location of its principal deposits and its chief uses. Among the more technical compilations may be mentioned a 67-page pamphlet on the "Antimony Deposits of Alaska," and a slightly larger paper on "Tungsten Minerals and Deposits." The Survey has also published from time to time in its reports special maps showing the distribution of the deposits of particular minerals.

The Survey's various publications are supplemented by extensive correspondence with the general public. The Survey is at all times ready to give available information to those inquiring into the occurrence and utilization of mineral substances. In this connection the report of the Director for

1916 says that the Survey "is becoming more and more a repository of information concerning the mineral resources of the country, much of which it furnishes through correspondence, giving detailed information which cannot be covered by publications, such as the location of deposits of minerals, both those that are developed and those that are undeveloped, and names of those who can supply the different minerals."

The numerous problems raised since the beginning of the war by the shortage of basic minerals have resulted in an unprecedented demand on the part of other agencies of the government for exact data as to the occurrence, production and utilization of these minerals. This demand the Survey has been able to meet by reason of its unique accumulation, over many years, of data of this type, and its trained organization ready to obtain new classes of data as new demands have been made for them.

Survey of Water Resources. In the course of its topographic and geologic surveys, and of its search for mineral deposits, the Survey, needless to state, collects a vast amount of information relative to the water supplies of the country; and its resulting topographic and geologic maps are of the highest value to one investigating the utilization of the water resources of any area covered by them. The Survey supplements the data collected and published in this connection, which have reference primarily to the location of the surface water supplies, with a survey designed to disclose also their quantity and quality, and to locate sources of underground supply.

The specific investigation of water resources by the Survey dates from the appropriations made in 1888 and 1889 for the investigation of the arid public lands and the extent to which they can be reclaimed by irrigation. The operations under those appropriations and the failure of Congress to make special appropriations for them between 1889 and 1894 were re

viewed in the preceding chapter. The investigation of water resources, however, was carried along on a small scale by special arrangements until 1894, when an appropriation authorized its extension to the whole country, and since that time the work has progressed steadily. The maintenance of hydrographic work on its present scale is made possible in large measure by substantial contributions made to the work by many of the states.

The operations embraced in the survey of water resources may be grouped under three heads-the location of supplies, the measurement of their quantity and the investigation of the practicability of their utilization. These operations vary essentially according as they deal with surface or ground

waters.

Surface Waters. The location of streams and springs is of course determined by the regular topographic surveys. Their quantity is determined by measuring their flow through a period of years sufficiently long to ascertain definitely the limits of variation, by maintaining stream-gaging stations over all the country, but particularly in the West. During the year ending June 30, 1917, nearly 1,200 such stations were maintained, but only thirty-six of them by the Survey alone, the others being maintained, in coöperation with the Survey, by various bureaus of the government (the Reclamation Service, the Forest Service, the Indian Service, the Weather Bureau, and others) and by states, cities and private persons. At these stations daily measurements of stream height are made, and periodic measurements of the flow or discharge. During the fiscal year 1917 an average of over six measurements of discharge were made per gaging station.

In addition to the data thus collected to determine the quantity of surface waters, analyses are made to determine their suitability for domestic, irrigation, boiler and other uses. In this work samples are usually taken from the stream daily for one year, united in sets of ten consecutive samples and the composite samples analyzed. The results of the analyses,