SEDIMENTARY

Scale: 6

1

1

Contour inter

Datum is mea

orh

62,500

2 miles

2

3 kilometers

erval 100 feet ean sea level

JULIUS BIEN & CO. LITH.N.Y.

TERTIARY

appropriate to the national organization. The application of the principles to particular ore bodies and camps is quite within reach of the individual mining engineers charged with development work.

That the Survey work does actually result in the development of these principles is evidenced by the simultaneous formulation by Emmons, Van Hise, and Weed of the doctrine of the secondary enrichment of metallic sulphides; by Emmons's statement of lateral segregation as applied to the genesis of the Leadville ores; by Van Hise's development of the principles of metamorphism in relation to ore bodies, and by many similar results.

The importance of aiding in the actual development of the resources of the country is constantly recognized, in two ways-first, by preparing handbooks and summaries of existing information regarding particular deposits or resources; second, by making careful structural studies of particular mining camps. Work of the first sort is exemplified in the series of papers, together presenting a succinct review of the coal resources of the United States, published in Part III of the Twenty-second Annual Report of the Survey; another such paper is that grouping all existing data regarding the asphalt deposits of this country, published in Part I of the same annual report. Similar papers covering the clay resources, Portland-cement materials, gypsum, etc., are in preparation. Studies of individual mining camps are constantly being made, a large number of the areas having already been surveyed either provisionally or finally.

In the early months of the development of a camp there are rarely sufficient exposures, either natural or artificial, to furnish data for a complete account of the ore bodies. Often at that time it is possible only to formulate general statements as to genesis and structure. Occasionally it happens that even after detailed studies have been made development is pushed so rapidly that still further details become available. Cripple Creek, which was the subject of a very careful study in 1894, is now being restudied in order to take advantage of the development of the district since that time; Leadville, also, which was the subject of an elaborate monograph in 1886, is being restudied, and probably other camps of the West will, in time, warrant similar resurveys.

For published results of the work of this division see the list of Survey publications, especially series A, B, C, D of the classification table.

DIVISION OF ALASKAN MINERAL RESOURCES.

HISTORY OF INVESTIGATIONS.

In 1895, through an appropriation by Congress of $5,000 for the investigation of the gold and coal deposits of Alaska, the Geological Survey for the first time was enabled to take up work in Alaska independent of other organizations. The same amount was appropriated