The standard series of colors for systems of sedimentary rocks is shown on the maps in the Survey's geologic folios but is subject to modifications for use on maps in other Survey reports. Each system is represented by a different color, and if there are two or more formations in one system they are generally distinguished by using different patterns composed of straight parallel lines in the same color. The patterns for subaerial deposits (chiefly Quaternary) are composed of dots or circles, or combinations of both, and may be printed in any color, but the color most often used is yellow or ochraceous orange. No specific colors are prescribed for igneous rocks, but if only a few areas are shown red or pink is preferred. The colors used for igneous rocks are generally more brilliant and purer than those used for sedimentary rocks. For small areas they are used "solid"; for large areas they are reduced in tone by the use of a suitable cross-line pattern or "reticle." Metamorphic rocks are represented by short dashes irregularly placed. These dashes may be in black or in color over a ground tint or over an uncolored area, or they may be in white on a ground tint or pattern. The standard colors used for the sedimentary series covering the 12 systems recognized by the Geological Survey are: Quaternary (Q), ochraceous orange; Tertiary (T), _yellow ocher_ and _isabella color_; Cretaceous (K), _olive-green_ or _rainette-green_; Jurassic (J), _blue-green_ or _niagara-green_; Triassic (TR), _light peacock-blue_ or _bluish gray-green_; Carboniferous (C), _blue_ or _columibia-blue_; Devonian (D), _gray-purple_ or _heliotrope-gray_; Silurian (S), _purple_ or _argyle-purple_; Ordovician (0), _red-purple_ or _rocellin-purple_; Cambrian (-C), _brick-red_ or _etruscan red_; Algonkian (A), _terra cotta_ or _onion-skin pink_; Archean (AR), _gray-brown_ or _drab_.[9] [Footnote 9: Names printed in italic are from "Color standards and nomenclature," by Robert Ridgway.] REDUCTION OF ENLARGEMENT OF MAPS.