52... Cn OK0e EXPLANATION OF THE COLOR CHWART FOR THE DESCRIPTION OF SEDIMENTARY ROCKS, PREPARED UNDER THE AUSPICES OF THE DIVISION OF GEOLOGY AND GEOGRAPHY, OF THE NATIONAL RESEARCH COUNCIL By Marcus I. GotpMAN and H. BE. MERwIN In preparing this chart colors were selected from Ridgway* with the aim to cover systematically the range of colors of rocks. These were arranged according to Ridgway’s system and reproduced as accurately as possible lithographically. In Ridgway’s system the numbers at the heads of the columns desig- nate the hues. The hue is the position of a color in the spectrum. Ridgway has selected from the spectrum 59 hues which he has named and numbered consecutively from 1 red to 59 violet. Thus, 11 is orange, 23 yellow, 35 green, and 49 blue. Intermediate hues are named by a combination of the names of the hues between which they lie, as for instance yellow-orange, orange- yellow, and so on, the last term of the combination being the name of the dominant hue. He arranged the hues in horizontal succession across the middle of the page. Upward from the middle, he made his colors lighter by adding white, designating the increasing whiteness by letters running from a tog. Downward he darkened his colors, designating the increasing dark- ening by letters running from h to n. In addition to this set of modified pure hues there are five sets of hues each made grayer than the preceding by the addition of increasing amounts of an intermediate neutral gray about like. next to the last neutral gray on the accompanying chart (Plate 2). The progressive graying is designated in Ridgway’s book by prime signs running from one to five, thus (’—”’’’’ ). Each hue thus grayed is then lightened and darkened like the pure hues. In addition to these sets of colors he has a column of neutral grays which are graduations between black and white. In selecting and arranging for this chart the colors from Ridgway, the plan was to reproduce entire columns and to arrange them in order of hues and under the hues in order of grayness from left to right. Technical diffi- culties in reproducing the colors, however, have made it necessary to elimi- nate some of the colorst and to depart somewhat from the regularity of Ridgway’s arrangement. The principles of his arrangement have, however, been retained. Two columns which fell out of place have been carried over with arrows to their proper position. In designating grayness, numerical exponents have been used instead of prime signs. The colors that have been the starting points for lightening upward and darkening downward, to which Ridgway gave no letter, have on this chart been designated by the letter 0, * Ridgway, Robert, Color standards and color nomenclature, Washington, D. C., pub- lished by the author, 1912. t The eliminated color squares have been printed over with aluminum. The approximate Ridgway equivalent is given in this modified form at the left of each color square, with the letter at the bottom, the hue number above it, and the exponent designating stage of grayness above that. Perfect agreement between these colors and Ridgway’s is not to be expected, because some of Ridgway’s colors having the same designation are appreciably different in different copies of his book, and the colors of the accompanying chart are slightly different on different sheets. But any of these differences are less than the observational errors in comparing rocks with the printed colors.. A sample of rock may not match any of these colors. But from a group of colors which it most nearly matches an approximate interpolation can be made and designated by intermediate symbols. Thus a color about midway between 6 m and 82k is 741. Or, to take a more complicated example: A rock more yellow than 18 but not quite as yellow as 21, grayer than 21? but not as gray as 21°, and between o and J in darkness, might be 2071/*h; or a rock between 1 and 8 in hue, and nearer 8, about as gray as 1° or 13°, and as dark as 7k or 871, might be 5°17. The designation by symbols is fundamental to the use of this chart. The symbol should always be given. Desirable as it is to convey the con- ception of a color to another person in some simple way, it seems that in the absence of generally disseminated and generally accepted standards this is not possible. Aside from the training it affords in the understanding of color, this chart will be of use mainly to the geologist himself and as a means of communication between those who use it either by itself or in conjunction with Ridgway’s book. The designation by the symbols of this System may be supplemented by verbal description, in which we believe the most fundamental term is the designation by hue. Thus “a medium gray dark reddish orange” (equal, for example, to 8*J) or “a slightly gray light -yellow”’ (equal, for example, to 211d). Certain popular terms, such as chocolate (Ridgway’s 7m), olive (212m), buff, (18°d), maroon, (1°m) may also be useful to supplement the designa- tion by Symbols. But the indefiniteness of most of them, unless used in a definite scheme such as Ridgway’s, should be realized. According to Ridgway’s investigations, “drab,” one of the very commonly used terms of this kind, is applied to a great range of colors clustering around 17‘ (near 18*a of the accompanying chart). i may be worth while to point out that browns are dark orange colors, than olive” is a dark yellow, and that the grayish reds of the type of 1%a to i, 1**/¢c to j are commonly thought of as purplish but are best not so described. In matching it is desirable to hold a small fragment of the rock close to the colors and to view them by diffused light coming from behind. We recommend that in the office, as far as possible, the use of this chart be supplemented by the use of Ridgway’s book, which may be had from A. Hoen & Company, Chester, Chase, and Biddle Streets, Baltimore, Maryland, for plus postage (shipping weight 2 pounds). The book has 1115 colors; this chart has only 114, Marcus I. GotpMAN, Chairman, H. E. MERwIN, Subcommittee on Color Chart of the Committee on Sedimentation of the Division of Geology and Geography, National Research Council. =O: ~ Nes OT et £5 gas 11 3-4 17 inven cata atta i N PLS IOV Wh Oe ETL I LMG RII SED NEI re ais 15".” 33 14% dl 13 (9-11)? t ; ® @ @ COLOR CHART FOR FIELD DESCRIPTION OF SEDIMENTARY ROCKS | NATIONAL RESEARCH COUNCIL, WASHINGTON, D. C. Prepared under the auspices of the Division of Geology and Geography by Marcus |. Goldman and H. E. Merwin, 1928 RIS 2 params Desa EID I EG ends penia iets ae 25 3-4 Be > : < : oe : 2 re. Pe ote o- MITA a peigeea opt —— 4 sf tS eae pee aes ee Ferd = 4 = ode BS ie nw - 2S z 3 + : POR Ea NTT Seas Hele Ai ens SRS a aheseppeg tron ences tne Uaioe tcp Sg aie PS rene be ahis 5 PRY TED serbintlre oessh te 9 APE a TRCN Foe rica chee at Acie tind nhetantiec obey Ribianontg 4-tauayan gs ye aes an a Oot a Rune ana Rests Ps srecnunsuas ® @ Ng COLOR CHART FOR FIELD DESCRIPTION OF SEDIMENTARY ROCKS NATIONAL RESEARCH COUNCIL, WASHINGTON, D. C. Prepared under the auspices of the Division of Geology and Geography by Marcus |. Goldman and H. E. Merwin, 1928