52 CLASSIFICATION OF THE PUBLIC LANDS. 



may be formed from the statement that on an average a township 

 (86 square miles) was completed by one man in four days. The fol- 

 lowing figures will also give some idea of the effectiveness of these 

 methods for the purpose which they were designed to accomplish. 



During the last six months of 1906 the total area withdrawn for 

 examination was approximately 66,000,000 acres, and by the close 

 of that year, as a result of, the field examinations, approximately 

 2,000,000 acres had been restored to public entry. During 1907 there 

 was an additional preliminary withdrawal of approximately 2,000,000 

 acres and by the end of the same year about 34,000,000 acres had been 

 added to the restorations. Thus, of the 68,000,000 acres withdrawn 

 during the first two years about 36,000,000 acres were restored as 

 noncoal land as a result of the rapid methods then used. Had the 

 Survey attempted a detailed study of these lands from the beginning, 

 there would have been much undesirable delay in the restoration of 

 large bodies of noncoal lands to entry. These early relatively inexact 

 methods were therefore well adapted to the ends they were designed 

 to accomplish. 



The principal areas of coal land having been outlined by, recon- 

 naissance surveys, attention was next turned to more unproved meth- 

 ods of. field work to meet the constantly growing need for better and 

 more detailed classification. The reconnaissance method was then 

 replaced by that in which plane table and telescopic alidade are em- 

 ployed. The most satisfactory alidade, which was designed by one 

 of the geologists engaged in the classification work, is a small instru- 

 ment carrying a telescope fitted with cross wires for stadia work and 

 a vertical arc for determining differences of altitude. 



The details of method used in plane-table mapping are varied 

 according to the topography and the forest conditions of the area 

 mapped, as well as according to the condition of the land survey. 

 In an area where there have been no land surveys or where those that 

 have been made are very poor, the triangulation or station method 

 is preferred, but stadia work only is practicable in certain areas— 

 for example, heavily wooded districts or regions cut by deep, narrow 

 canyons. Either method, however, gives excellent results, for by 

 either the coal outcrop is actually traced in the field and the exact 

 horizontal and vertical positions are determined for every observa- 

 tion. In connection with these- precise locations full data are pro- 

 cured on the character of the coal. If the region is undeveloped and 

 no coal mines or prospect pits are available for examination, open- 

 ings are made and sections are measured wherever such work is neces- 

 sary to give adequate data for classification. 



Perhaps the most detailed work that is now being done in the 

 coal areas is that carried on in those districts where the geologist 

 works in conjunction with the topographer. This method results in 



