30 INDEX TO THE STRATIGRAPHY OF NORTH AIMERICA. 



Although for some maps these visible patterns may be costly there may also 

 be economy in their use, as stated below. A consideration which rises to the impor- 

 tance of a principle in devising any general color scheme relates to economy. 

 Economy in reproduction is usually secured by limiting the number of printings. 

 There are two ways in which this may be done — (a) by using patterns of one color 

 which produce distinctions of tint; (h) by overprinting two or more colors. In 

 applying the former method the preparation of a lithographic stone so that it shall 

 print many devices in one color, yet shall give different effects, may occasion greater 

 cost than would be involved in printing from two or more simpler stones. In 

 applying the second method, the combinations secured by overprinting two or 

 more colors are numerous and may be less monotonous than those obtained by 

 patterns of one color. The lithographer has always to balance the cost of preparing 

 stones and that of printing, and the calculation of least expense involves not only 

 the number of effects required but also the size of the edition and other factors. 

 The conditions vary with individual maps, and an economical color scheme for 

 general use must permit the employment of either or both methods. 



By coloring geologic maps according to the proposed principles, we may secure 



(a) legibility, because the invariable order of colors will indicate the order of age; 



(b) common usage of colors within limits, which may be wide, for freedom is impera- 

 tive, but which are nevertheless significant; (c) recognition of customary usages 

 that now exist but are often disregarded; and, consequently, (d) the equivalent of 

 a universal language in the coloring of all maps that follow the accepted principles. 



The accompanying geologic map of North America represents an application 

 of the proposed principles to a general case of great complexity. It is hoped that 

 it may serve to encourage consideration and adoption of a universal color language 

 on geologic maps. 



CONTRIBUTORS. 



The list of contributors to the geologic map of North America and of the sources 

 from which it has been compiled follows." 



In this list are included the names of authors of geologic maps, published and 

 in manuscript, used in compiling the map of North America, and those who fur- 

 nished data, published and unpublished, for the correction of previously existing 

 maps, or contributing to the knowledge of little-known regions. The sources of 

 information from which published maps were originally derived are not given except 

 where specifically credited on the maps. The term "folio" in the citations refers 

 to the Geologic Atlas of the United States, pubUshed by the United States Geo- 

 logical Survey. 



Adams, F. D. 



Member of the committee on pre-Cambrian nomenclature. 



Data on Victoria, Peterborough, and Hastings counties: Ann. Kept. Geol. Survey Canada for 1892-93, vol. 6,. 



Kept. J. 

 Montreal sheet: Ann. Kept. Geol. Survey Canada for 1894, vol. 7, Kept. J. 

 Geologic map of I.aurentian area north of the Island of Montreal: Ann. Rept. Geol. Survey Canada for 1895, 



vol. 8, Rept. J. 



a This list has been prepared by G. W. Stose and (for the Canadian contributors) J. M. Nickles, from notes and lists 

 by Bailey Willis and the Canadian Geological Survey and from other soiuces. 



