44 



MARINE BOTTOM SAMPLES OF LAST CRUISE OF CARNECaE 



The lack of intensity, that is the amount of neutral gray 

 in any color, may be shown by a small exponential num- 

 ber, which increases from 1 to 5 with increasing amounts 

 of gray: thus 173b indicates a color nearly intermediate 

 between orange and yellow in hue, having admixtures of 

 9.5 per cent white as measured by a color wheel and 77 

 per cent neutral gray measured by the same means. In 

 addition to the numerical descriptions of the colors, 

 every alternate hue and admi.xture of white or black and 

 each increment of neutral gray is indicated by a distinct 

 name. Ridgway's system of color classification is the 

 basis of Goldman and Merwin's (1928) color chart, and 

 these authors recommend the use of Ridgway's book 

 when it is available. 



The color of a sample was determined, except in the 

 case of very incoherent muds and oozes, by placing a 

 small part on a knife blade and holding it directly above 

 the colored paper in Ridgway's book with which it was 

 being matched, always as nearly as possible at the same 

 angle to the eye of the observer. Most of the Carnegie 

 samples are homogeneous in appearance, and therefore 

 could be compared fairly accurately with a homogeneous 

 surface of colored paper, but for coarse-textured sam- 

 ples it was necessary to make a crude approximation to 

 homogeneity by trying to blend visually the various color 

 components which were evident. 



Sumner (1927) has outlined the limitations of sets of 

 standard colors such as Ridgway's and the necessary 

 conditions for their use. He points out that it is impos- 

 sible to make determinations which are quantitative in 

 the sense of being expressible in significant figures 

 through any system of matching standards. Further- 

 more, colorimetric tests made by him on many of the 

 plates of Ridgway's book show some wide discrepancies 

 between colors which are said to be of the same hue or 

 to have the same amount of dilution with white. He 

 states, however, that plates XV, XXIX, and XL, which 

 happen to be the principal ones used in the determination 

 of the colors of deep-sea sediments, seem to conform 

 fairly well with each other, at least in respect to hue. 



Besides the inaccuracies inherent in the method of 

 color comparison used, there are certain sources of er- 

 ror peculiar to the material observed, namely, those 

 due to (1) possible changes in color after collection and 

 during storage, and (2) differences in color due to the 

 amount of water present. 



It is not believed that the colors of the red clays or 

 Globigerina oozes in the collection suffered any marked 

 changes except those incident to the unavoidable drying 

 of some samples during storage. Only very rough color 

 determinations were made on board and these are given 

 in table 1, column 9, in the extracts from the field notes 

 made at the time of collection, but Dr. E. G. Moberg, 

 who was on board the Carnegie between San Francisco 

 and Hawaii, has kindly compared some of the samples of 

 red clay from this region with his memory of their con- 

 dition when collected, and he does not believe that any 

 marked color differences exist. On the other hand, a 

 few of the terrigenous samples, which probably contained 

 considerable amounts of decomposable organic matter, 

 have, perhaps, suffered more or less decided color 

 changes. 



The samples when examined had widely differing 

 water contents, which differed also from the amounts of 

 water originally present in them: some were quite dry; 

 in others partial drying had taken place and the samples 

 were only slightly moist; still others, especially many 



red clays, appeared to have approximately their original 

 amount of water; whereas in others considerable water 

 had been added during handling. Since color is so large- 

 ly dependent on water content, only those samples of ap- 

 proximately the same state are comparable. The sam- 

 ples are recorded as being either (1) dry, (2) moist, 

 when the original interstitial water content is largely or 

 partly present, or (3) wet, when water has been added 

 and the sediment has obviously been shaken up several 

 times and dispersed in it. 



When the samples were stored in two or more bot- 

 tles, the material in one bottle would often "be moist, 

 whereas in another it would be dry, and in these cases 

 the color in both the moist and dry states is recorded. 

 A comparison of such determinations shows that in Glo- 

 bigerina oozes the dry part of a sample may be from 

 two to seven shades lighter than the corresponding wet 

 part. The hue is often unchanged, but sometimes the 

 dried material is slightly more reddish, probably owing 

 to partial dehydration of the hydrated oxides of iron 

 present in the sediments. Red clays become six to nine 

 shades lighter when dried and about 1° more gray, but 

 there is usually no change in hue, although sometimes 

 they become less reddish. 



The importance in classification of the colors of ma- 

 rine sediments has been discussed on pages 5 and 6. In 

 two other recent papers on marine sedimentation attention 

 has been paid to the factors affecting color. Pratje (1931), 

 who has employed Ostwald'sl system and standards of 

 color nomenclature (which are fundamentally the same 

 as Ridgway's) in describing the sediments of the Ger- 

 man Bight of the North Sea, points out that these deposits 

 exhibit only a small range of color, in spite of the wide 

 variation in sedimentary types. He claims that the con- 

 tents of organic matter and calcium carbonate, together 

 with the states of oxidation of the iron compounds, are 

 the factors most closely related to color in such terrig- 

 enous deposits. Gorshkova (1931) has studied the sig- 

 nificance of color in the bottom deposits of the White and 

 Barents seas. The variation from brown through gray to 

 greenish gray in the colors of these sediments was found 

 to be accompanied by a decrease in their contents of iron, 

 manganese, and phosphate, and a corresponding increase 

 in organic matter and sulphur, together with a change 

 from predominantly ferric to predominantly ferrous iron. 

 The greenish gray deposits contain from five to fifteen 

 times as much living matter as the brown soils. 



The Carnegie samples, like those of Pratje and those 

 of Thorp (1931), exhibit a small range of color. The total 

 variation in moist samples is between IS^l (yellowish 

 orange in hue, containing 80 per cent of black and 58 per 

 cent of neutral gray) for sample 49, a south Pacific red 

 clay; and 2l4b (orange-yellowish yellow in hue, with 9 

 per cent white and 90 per cent neutral gray, called light 

 grayish olive by Ridgway) for sample 34, a green clayey 

 mud from off the South American coast. 



Certain red clays from the south Pacific, namely 

 samples 30, 38, 47, 48, 49, and 50, are the reddest and 

 darkest of the sediments collected (excluding nonrepre- 

 sentative samples and rock fragments, such as samples 

 11, 75, and 78). When moist they exhibit colors between 

 15^1 and 17 m (orange yellow, with 87.5 per cent black, 

 called raw umber by Ridgway). Two other red clays 

 from the south Pacific, samples 31 and 35, collected near 



lOstwald, Wilh., Farbtonleiter 2. Afl. Verlag 

 Unesmag.m.b.H, Leipzig, quoted by Pratje. 



