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2. Geologic surveys in various portions of the United States.

3. Chemical and physical researches relating to the geology of the United States, including researches with a view of determining geological conditions favorable to the presence of deposits of potash salts.

4. Investigation of the mineral resources of Alaska. 5. Preparation of a report on the mineral resources. of the United States.

6. Gaging streams and determining the water supply of the United States, the investigation of underground currents and artesian wells, and the preparation of reports on the best methods of utilizing the water resources.

7. Discovering, developing, protecting and rendering more accessible springs, streams and water holes on arid public lands of the United States; erecting and maintaining monuments and sign boards and providing ready and convenient means by which water may be brought to the earth's surface.

8. Examination and classification of lands requisite to and suitable for enlarged homesteads, stock-raising homesteads, public watering places and stock driveways. as required by the public land laws.

The scope of the activities thus authorized is of course dependent upon the amount of the appropriation. As will hereafter be noted, the act further controls the scope of some specific activities by a special provision regarding the manner of the utilization of the amount appropriated.

For a clearer presentation the activities of the Survey may be regarded as falling under the following seven heads:

1. Geologic surveys and investigations.

2. Compilation of information relative to the mineral industries.

3. Topographic surveys.

4. Surveys and investigations relative to water re

sources.

5. Examinations, under act of March 1, 1911, of land proposed to be purchased by the government for the protection of navigable streams.

6. Investigations of the character and value of public lands made necessary by the land laws.

7. Operation of lithographing and engraving plant.

As the purpose of the larger part of the Survey's work is the acquisition and dissemination of knowledge concerning geography, geology, mineral resources, and water resources, most of its activities, therefore, involve the publication of the results achieved.

Topographic Survey. As already indicated, the Survey is engaged in making and publishing a topographic atlas of the United States that is, a series of maps exhibiting the configuration of the land and water, the elevations of the land, and the principal features of culture. In addition to these atlas sheets it is publishing special maps of certain areas such as the areas including large cities.

The work on the topographic atlas was begun by the Survey in 1882, promptly upon the enactment of the provision of law authorizing the Survey to prepare geologic maps of the United States. In entering upon the task, one of unprecedented magnitude, of executing a topographic survey of the entire United States, the Survey fell heir to the results which had been produced by previous topographic surveys, federal, state and private. Notable among these results were the maps produced by the several geographical and geological explorations and surveys of the West, to which reference was made in the preceding chapter. The materials thus acquired were of very unequal value, but they furnished a point of departure for the Survey's work.

The Survey did not for some years attempt to publish topo

graphic maps for general distribution, but supplied them only. to its own members and to other government services. Authority to sell the maps to the general public was finally granted by Congress in 1897 (act of February 18, 1897, 29 Stat. L., 701).

During the first few years of the Survey's map work it continued to use the same scale that had been employed by the earlier independent surveys-about 4 miles to the inch, or 1:250,000, with relief shown by 200-foot contours; but when the coöperative surveys of the states were begun it was seen to be desirable to increase the scale and decrease the contour interval, not only for the work in those states, but for that in other states in which coöperation was not being carried on.

The earlier topographic mapping of the Survey was subjected to some criticism on account of lack of refinement in detail. It was a question of judgment whether the appropriation should be expended in accurately mapping a limited area or in making reconnaissance surveys over a more extended area. The less accurate maps were less expensive, and served a useful purpose in establishing the value of topographic surveys. The results have proved the wisdom of a policy whereby the people were gradually educated to the use of refined and detailed maps, while Congress learned to appreciate the cost and the comparative slowness with which accurate surveys would be prosecuted over so vast a territory as that of the United States. Had fewer square miles been mapped annually in the early years, but with the accuracy attained at present, it is doubtful if Congress would have continued to maintain the organization. As it was, valuable results were rapidly put forth, and in time it has been possible to supersede the older reconnaissance maps with more detailed maps.1

As the topographic work steadily advanced, not only in the area covered, but in accuracy, it was found desirable to obtain from Congress authority to run careful spirit-level lines. and to establish bench marks for permanent record of eleva'U. S. Geological Survey, Bulletin No. 227, 1904, p. 57.

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