topographer, or even at times works in advance of formal topographic mapping, but in such cases he is either supplied with some form of map, or himself constructs a rough topographic map as he works.

The field work of the geologist engaged in systematic geologic survey is ordinarily confined to examination of the surface, aided by magnetic observations in connection with magnetic ores. Samples of rocks and ores and specimens of fossils are collected. All mines or other available openings are also examined, but only in exceptional cases are independent borings made for this purpose. The field work is supplemented by office and laboratory work, which includes microscopic and chemical examinations of the rocks and ores collected and paleontologic study of the fossils.

The results of the geologic surveys are given to the public in reports accompanied by geologic maps, diagrams and other illustrations, and in "geologic folios" containing maps and descriptive text. These reports vary widely in scope and character, dealing in some cases with selected areas, in others with selected deposits, and in still others with particular geologic problems. They vary also in size and in the degree of technical knowledge assumed on the part of the reader. The shorter and less technical reports are published under the general name of Bulletins, those of intermediate character under the name of Professional Papers, and the more voluminous and technical treatises under the name of Monographs. The Bulletins and Professional Papers are distributed free for the public, while Monographs are sold.

More recently, the Survey has been issuing, as Bulletins, guidebooks to various parts of the western states, arranged according to the principal tourist routes. Although the geologic features of the country occupy a large part of the text, information is also given, in popular style, relative to the geography, including scenic features, notable historic events, Indian tribes, industrial resources and plants and animals.

A "geologic folio" is thus described by the Survey: 2

A standard geologic folio comprises a descriptive text, in which the geography, topography, and geology of the area are described; a topographic map; a geologic map, printed in colors, showing the areal distribution of the geologic formations; a geologic map showing the deposits of economic value in stronger or more brilliant colors; a geologic map on which the underground structure of the rocks is exhibited by vertical sections representing what would be seen in deep trenches cut across the area; and a columnar section, in which the rocks are represented in a vertical column in their normal relation one to another, accompanied by a condensed description of their composition, thickness, and relations.

For special areas other maps or illustrations are included. Often it is desirable to present with the description a page of illustrations reproduced from photographs or sketches. For artesian-water areas the distribution of the water-bearing strata, the areas where flowing water may be obtained, and the depths to the water horizon are shown on a special sheet. For active mining regions a map on a scale sufficiently large to show important details of the geology, mines, and ore deposits is inserted. For coal regions of economic importance special methods are used to show the structure or lay of the coal beds of so much importance to the mine worker. This is done by means of contour lines which show the elevation above sea of the coal bed throughout its occurrence in the area, and then furnish the data for determining the depth of the coal below the surface at any point. Sections of coal beds which have been opened or worked are shown on a large scale and their relation to one another is indicated.

Generally speaking, each folio relates to a single quadrangle, that term having the same meaning as when applied to a topographic map; but some folios cover two or more quadrangles.

Occasionally, the advance of geologic knowledge of a particular area, or the demand for more detailed information, necessitates a revision of maps already published.

The geologic survey now carried on discloses the distribu2 The U. S. Geological Survey: Its Origin, Development, Organization and Operations, p. 99-100, 1904.

tion and thickness of the formations in the area covered, their chemical composition and physical characteristics, and their age—that is, the period of geologic time in which they were deposited, as well as their form-that is, their structure, and the geologic forces which caused their deposition, erosion, and deformation.

The value of facts regarding the mineral character of rock formations for the development of mineral resources need not be dwelt upon. In disposing of the public lands this information is useful not only in shaping policies but in administering the land laws, and such information concerning lands privately owned facilitates and expedites the development of mineral deposits of economic value, or indicates the non-existence of such deposits. In this connection it may also be pointed out that information as to rock formations incidentally includes information as to underground water.

The identification of the geologic positions of several strata in the geologic time-scale is also of value to the economic geologist, as it helps him to determine the probability of the occurrence, in the area, of particular economic deposits. Another value, however, lies in the light it throws on the relation of the geology of the area to that of adjacent areas and, ultimately, of the entire country.

The maps and descriptive texts resulting from geological surveys find a most important use in the hands of the Survey itself in its work of land classification and of geologic research.

It would be difficult to ascertain precisely the total amount spent by the Survey in geologic surveys of the country. The appropriations used have been made under various heads, and some have provided for other work than geological surveys. The total amount appropriated since 1889 for "geologic surveys in various portions of the United States" has been about $5,500,000; that appropriated for paleontologic researches (an item of appropriation no longer in use), and for chemical and physical researches has been over $900,000; and that ap

propriated for "geologic maps of the United States" has been nearly $2,500,000. To this there should be added a large part of the "lump-sum" appropriations made to the Survey during 1879-1888. It seems fair to conclude, therefore, that the geologic surveys proper, exclusive of surveys in Alaska, have cost nearly $9,000,000.

Investigation of Mineral Deposits. In addition to its surveys of selected areas, the Survey makes many investigations and surveys with a view to determining the occurrence and distribution of the deposits of a particular mineral, or the mineral deposits in a particular area. Much of this work that is done on the public lands is a direct incident to the task of classifying or evaluating those lands under the land laws, and this phase of the work will be discussed in a subsequent section.

The investigations here considered are thus concerned only with a single class of mineral deposits. Though the Survey's work in Alaska has from the beginning been conducted under appropriations for the "investigation of the mineral resources of Alaska," no specific phrase of that kind has ever been used in appropriation bills covering investigations in the United States, which have been conducted under the general authorization for "geologic surveys." Investigations of this type are generally undertaken by the Survey with reference to a deposit of major importance in a field not yet adequately exploited. The Survey attempts to outline the limits of the area in which occurrences of the deposit may be expected, and to indicate the zones in which the richest deposits are likely to be found and the general conditions to be expected. An investigation of this type is the Survey's work on the oil shales of the Green Bay region.

The Survey also, when an unusual demand arises for any mineral product, makes a general investigation of the occurrence of that mineral. Investigations have thus been made of such minerals as monazite, zircon, iridosmine, platinum,

and all minerals possessing radio-active and radio-responsive products. More recently a systematic search has been made for new deposits of petroleum, phosphates, nitrates, potash, pyrites, and manganese.

For the proper conduct of exploratory researches of this kind, and indeed for the most effective collection of data relative to mineral deposits in the course of general geologic surveys, it is essential that the geologists conducting the operations be thoroughly versed in the technology of the production of the mineral sought.

Recognizing that the ability to form a correct judgment as to the practical utilization and value of an ore or other mineral deposit in the ground is most effectively acquired through the field observation of operating works and processes for the exploitation and reduction of the same or similar deposits, the Survey regards it of the highest importance that the geologists who may be called upon to appraise undeveloped mineral resources in the public domain or in other regions of the country shall keep as closely as practicable in touch with the mineral industry, and shall have a knowledge of the factors conditioning the successful treatment and utilization of the ores he is examining.3

The methods employed in searching for new deposits are not unlike those followed by private prospectors possessed of adequate funds and acting under the advice of trained geologists. If possible, coöperative arrangements are made with private parties who may be drilling in the areas selected for exploration or in adjacent areas by which the cores removed by their drills are turned over to the Survey for examination and report. This method has been employed most consistently in connection with the search for potash deposits which the Survey has been making for several years. Describing this coöperation, the report of the Director for 1915 states:

4

3 Report of the Director of the Geological Survey, 1915, p. 47. 4 P. 44.