60 CLASSIFICATIOlir OP THE PUBLIC LANDS. 



corners accurately with instruments, and the elevation of each point 

 is ascertained, so that the underground relations of the bed can be 

 determined. 



The number of sections measured along the .outcrop of the bed de- 

 pends on the local conditions. If the bed is variable it must be ex- 

 amined at short intervals, but if it is regular the measurements may 

 be made farther apart. Some records show measurements only 50 

 feet apart, whereas others are half a mile or more, though a shorter 

 distance is recommended. There is no definite number of measure- 

 ments to the township. In some townships few are made, whereas 

 in others there are as many as a hundred. 



At the same time that the geologist is examining the field he pro- 

 cures any information which may have been obtained by miners, pros- 

 pectors, well drillers, or others making excavations. Such informa- 

 tion ordinarily consists of records of wells, drill holes, and mine 

 shafts, mine maps, both exterior and interior, records of production 

 and use, etc., and is of great value in the proper classification of the 

 land. 



This method may be applied equally well to materials other than 

 coal if they occur in or in a definite relation to stratified beds, and 

 with modifications it may be and is adapted to less regular deposits 

 of metalliferous minerals. Its chief application, however, in actual 

 Survey practice is in the coal fields of the plains region, where the 

 recent and more accurate Land Ofiice plats are available as bases. 



RECONNAISSANCE SURVEY. 



Reconnaissance surveys are ordinarily only preliminary and those 

 made for purposes of classification are intended to determine the 

 general distribution of the mineral deposits in areas which have not 

 been described by geologists or which may have been examined only 

 casually or with some other problem in mind than that of dis- 

 covering minerals of economic value. If no reliable information is 

 at hand concerning an area containing public land, a geologist makes 

 a reconnaissance to determine the best method of work to be followed 

 if minerals are found. 



The method of reconnaissance varies with the character of the 

 country to be examined. If the country is suitable for the use of the 

 plane-table method of surveying, the geologist uses that method. He 

 proceeds in the manner already described but on a smaller scale and 

 with less detail. If the country can be readily crossed and little accu- 

 racy is required, the geologist starts with an assistant and travels by 

 buggy to the points to be examined. He determines his location from 

 traverses based on hand-compass readings to give direction and on 

 counted revolutions of the buggy wheel to give distance. These 

 traverses are tied to known points wherever possible, and the inter- 



