50 CLASSIFICATION OF THE PUBLIC LANDS. 



layed. The present withdrawals are a temporary expedient whose 

 employment should be rendered unnecessary as soon as possible. It 

 can not be economically advantageous to the country to have mil- 

 lions of acres of lands, valuable for petroleum, phosphate, or potash 

 or for power or reservoir sites, absolutely segregated from all forms 

 of disposal for an indefinite period. Some of the lands have already 

 been so withdrawn for nearly four years. Congress should be fully 

 informed concerning all the factors to be considered, but it should 

 also act promptly. 



CLASSIFICATION OF MINERAL LANDS. 



FIELD METHODS. 

 DEVELOPMENT. 



Since the United States Geological Survey was organized the 

 methods it employs in its diverse field investigations have gradually 

 become more refined and more precise. If a topographic majs made 

 by the Survey 20 years ago is compared with one of its recent maps 

 the difference will be patent even to the untechnical critic, yet many 

 of the important improvements adopted during that period do not 

 appear on the map. The closer and more accurate triangulation 

 net, the great increase in the numbers of intersected points and of 

 level lines, and the general completeness of both vertical and hori- 

 zontal control are not directly reproduced on the completed sheet, 

 but they have been used in its preparation and»give it far greater 

 accuracy and expressiveness than the earlier maps. The methods 

 employed by the engineers of the water-resources branch and by 

 the geologists of the geologic branch have likewise undergone steady 

 and consistent development. 



Perhaps nothing in recent years has so directly stimulated the em- 

 ployment of more precise methods in field work than the require- 

 ments of land classification, and the development here is well ex- 

 emplified in the work done by the coal geologists. The law under 

 which coal land is classified, unlike the laws controlling the classi- 

 fication of lands containing other mineral resources, requires a valu- 

 ation of the land. It is therefore especially necessary to trace the 

 outcrops of coal beds with exactness and to fix their relations to the 

 units of the public-land surveys by precise methods. This has led 

 to the introduction of refinements that are not generally considered 

 necessary in preparing a geologic folio or in determining the general 

 relations of the formations in any region. It is perhaps worth while 

 to trace a part of this development of the field methods employed in 

 the classification of coal lands, as an example of a general improve- 

 ment and as an introduction to a discussion of the methods now 



