40 THE U. S. GEOLOGICAL SURVEY 



topographer, or even at times works in advance of formal 

 topographic mapping, but in such cases he is either supplied 

 with some form of map, or himself constructs a rough topo- 

 graphic map as he works. 



The field work of the geologist engaged in systematic geo- 

 logic survey is ordinarily confined to examination of the sur- 

 face, aided by magnetic observations in connection with mag- 

 netic ores. Samples of rocks and ores and specimens of fos- 

 sils are collected. All mines or other available openings are 

 also examined, but only in exceptional cases are independent 

 borings made for this purpose. The field work is supple- 

 mented by office and laboratory work, which includes micro- 

 scopic and chemical examinations of the rocks and ores col- 

 lected and paleontologic study of the fossils. 



The results of the geologic surveys are given to the public 

 in reports accompanied by geologic maps, diagrams and other 

 illustrations, and in "geologic folios" containing maps and de- 

 scriptive text. These reports vary widely in scope and char- 

 acter, dealing in some cases with selected areas, in others with 

 selected deposits, and in still others with particular geologic 

 problems. They vary also in size and in the degree of tech- 

 nical knowledge assumed on the part of the reader. The 

 shorter and less technical reports are published under the gen- 

 eral name of Bulletins, those of intermediate character under 

 the name of Professional Papers, and the more voluminous 

 and technical treatises under the name of Monographs. The 

 Bulletins and Professional Papers are distributed free for the 

 public, while Monographs are sold. 



More recently, the Survey has been issuing, as Bulletins, 

 guidebooks to various parts of the western states, arranged 

 according to the principal tourist routes. Although the geo- 

 logic features of the country occupy a large part of the text, 

 information is also given, in popular style, relative to the geog- 

 raphy, including scenic features, notable historic events, In- 

 dian tribes, industrial resources and plants and animals. 



