442 G. K. Gilbert — Congress of Geologists. 



resolutions a' partial scheme has been selected, one color at a 

 time, and the completion of the plan has been left to the com- 

 mitte on the map of Europe. That committee has prepared a 

 color legend, which is accessible to American geologists in the 

 volume of information published by the American committee. 

 It is understood in a general way that the Congress reserves 

 final action, and the published legend not only belongs speci- 

 fically to the map of Europe, but is provisional ; still, as this 

 map, if generally approved, will unquestionably be declared by 

 the Congress an authoritive pattern for the guidance of map 

 makers, the plan should be freely criticised at its present stage. 

 The selection of uniform colors is a far more delicate and im- 

 portant matter than the arrangement of taxonomic terms; for 

 while ill-chosen words may quickly fit themselves to new uses, 

 the adoption of an ill-arranged color scheme must entail contin- 

 ual loss. 



In my judgment the scheme provisionally chosen is defective 

 in several particulars, to which I shall presently call attention, 

 but it is neccessary to introduce the discussion by a statement 

 of the conditions to be satisfied by a standard color scheme and 

 a statement of the practical means available. The following 

 are the principal conditions, arranged in an order embodying 

 my estimate of their relative importance: 



(1). The map must be clearly and easily legible. Each 

 color must be so distinct from each other color that it can be 

 identified, whatever its surroundings; and all other conven- 

 tions must be readily discriminated. 



(2). The cartographic scheme must be adjustable to the geo- 

 logic facts; it must not require that the facts be adjusted to it. 



(3). The same scheme should serve both for general maps, 

 as, for example, those representing only systems, and for detail 

 maps, representing numerous smaller divisions. 



(4.) Undue expense should be avoided. The amount and 

 consequent utility of color cartography is largely limited by its 

 cost. 



(5). It should be easily fixed and retained in the mind. This 

 is best accomplished by making it orderly. 



(6). Other considerations permitting, the map should please 

 the eye. Since the arrangement of color areas cannot be fore- 

 told, this can only be accomplished by admitting a certain range 

 of choice. If allowed sufficient latitude in the selection of 

 tones, an expert colorist can ameliorate an offensive combina- 

 tion of hues. 



(7). Other considerations permitting, the establishment of a 

 universal system should involve the least possible inconven- 

 ience. But as the inconvenience of change is temporary, while 

 the inconvenience of a bad system is lasting, this consideration 

 should yield to every other. 



