COLOE SCHEME. 21 



complex a map and to engrave and lithograph it according to the high standards 

 of modern cartography. The writer has been fortunate in being associated with 

 the Sm-vey's editor of geologic maps, Mr. G. W. Stose, and aided by the chief 

 engraver, Mr. S. J. Kiibel. To them in particular and also to Mr. H. S. Selden, 

 who drew the manuscript geologic map, and to the cartographic section of the 

 Survey he would express his indebtedness. 



The names of the contributors to the map are given in the list at the close of 

 this introduction. There are, however, certain portions of the geologic map which 

 are strikingly different from any previously published and which represent original 

 contributions from geologists who are familiar with special districts. These 

 contributions are especially acknowledged as follows : 



Mr. Robert T. Hill prepared an original map of Sonora and Chihuahua, Mexico, 

 and of portions of adjacent areas in the United States. 



Messrs. T. W. Vaughan and A. C. Spencer furnished the map of Cuba according 

 to published data and their own unpublished notes. 



Mr. W. P. Blake supplied material for the little-known districts of Arizona 

 and his map was adjusted to notes and maps supplied by other geologists. 



Mr. Ralph Arnold prepared for the geologic map of North America issued 

 by the International Geological Congress in 1906 the map of California south of San 

 Francisco, and for the map accompanying this volume Mr. Robert Anderson reviewed 

 this material and supplemented it from his own notes. 



Mr. A. C. Lawson supplied a manuscript map of the northern Coast Ranges, 

 which was adjusted to other data in hand. 



Mr. T. Wayland Vaughan and Mr. L. W. Stephenson drew the map of the 

 Atlantic and Gulf coastal plains according to cooperative work in progress in the 

 several States. 



Mr. Arthur Keith prepared the map of the Appalachian Mountains from 

 Maryland to Georgia, east of the Appalachian Valley, after his own surveys, sup- 

 plemented by the original work of other geologists. 



Messrs. George Otis Smith and E. S. Bastin compiled the map of the New 

 England region from surveys by several geologists, supplemented by their own 

 original notes. 



Mr. N. H. Darton, Mr. M. R. Campbell, and the geologists assisting Mr. Camp- 

 bell supplied the data for the Mesozoic and Tertiary of Colorado, Wyoming, and 

 Montana. 



COLOR SCHEME. 



PRINCIPLES. 



Color is used on geologic maps to delineate the distribution of various rocks. 

 Legibility is the first requirement, economy in printing the second, and good taste 

 the third. Custom may prescribe certain associations of color with particular 

 implications, which, being thus established, control other associations. 



The requirement of legibility determines the first principle. Distinctions 

 of color should be so marked as to be clearly recognized. As contrast depends 

 on hue and tint or shade in flat colors, and also on pattern where devices are 

 employed, distinctions of hue, tint, shade, or pattern may be used to produce it. 



