10 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 11)02. [bull. 213. 
vey in the investigation of any particular group of mineral products. 
They are generally confined to Survey publications, though a few 
titles of important papers published elsewhere by members of the 
Survey are included. 
The results of the Survey work in economic geology have been 
published in a number of different forms, which are here briefly 
described : 
1. Papers and reports accompanying the Annual Report of the 
Director, United States Geological Survey. — Prior to the present year 
many economic reports were published in the ro}^al octavo cloth-bound 
volumes which accompanied the Annual Report of the Director. 
This form of publication for scientific papers has been discontinued 
and a new series, termed Professional Papers, substituted. 
2. Bulletins of the United Slides Geological Survey. — The bulletins 
of the Snrve} T comprise a series of paper-covered octavo volumes, 
each in general containing a single report or paper. These bulletins, 
formerly sold at nominal prices, are now distributed free of charge t 
those interested in the special subject discussed in an}^ particula 
bulletin. This form of publication facilitates promptness of issue for 
economic results, and most economic reports are therefore published 
as bulletins. Their small size, however, precludes the use of large 
maps or plates, and reports containing large illustrations are there- 
fore issued in the series of Professional Papers. 
3. Professional Papers of tin United States Geological Survey.— 
This series, paper covered, but quarto in size, is intended to include 
sueh papers as contain mapsor other illustrations requiring the use of 
a large page. The publication of the series was commenced in 1002, 
and the papers are distributed in the same manner as bulletins. 
4. Monographs ofthi United States Geological Survey. — This series 
consists of cloth-bound quarto volumes, and is designed to include 
exhaustive treat iseson economic or other geologic subjects. Volumes 
of this series are sold at cost of publication. 
5. Geologic folios of the United Stoics Geological Survey. — Under 
the plan adopted for the preparation of a geologic map of the United 
States the entire area is divided into small quadrangles, bounded by 
certain meridians and parallels, and these quadrangles, which num- 
ber several thousand, are separately surveyed and mapped. The | 
unit of survey is also the unit of publication, and the maps and 
descriptions of each quadrangle are issued in the form of a folio. 
When all the folios are completed thej T will constitute a C4eologic 
Atlas of the United States. 
A folio is designated by the name of the principal town or of a 
prominent natural feature within the quadrangle. It contains topo- 
graphic, geologic, economic, and structural maps of the quadrangle, and 
occasionally other illustrations, together with a general description. 
Under the law, copies of each folio are sent to certain public libra- 
ries and educational institutions. The remainder are sold at 25 cents 
