DESCRIPTION OF SAMPLES 



45 



the South American coast, are lighter and more grayish 

 in color. It is noteworthy that sample 31 is relatively 

 high in nitrogen for a pelagic deposit, therefore presum- 

 ably in organic matter. On the other hand, the amount, 

 kind, and state of oxidation of iron and manganese com- 

 pounds are probably the controlling factors of color in 

 Pacific pelagic deposits. These are not functions of the 

 total organic matter content of a sediment, but rather 

 may, in part at least, be dependent on the amount of de- 

 composable organic materials which it contains. The 

 latter, in turn, is dependent on the origin and relative 

 rate of deposition of organic matter. 



The darkness and intensity of the brown colors of 

 south Pacific Globigerina oozes are directly proportion- 

 al to their contents of manganese and iron. Samples high 

 in these substances also tend to be high in phosphate, in 

 agreement with the findings of Gorshkova, but there 

 seems to be little correlation with the organic matter 

 contents. These relations are indicated in table 3 (page 

 41), which gives a comparison of the color values shown 

 in table 1 with the amounts of Mn02, Fe203, P2O5, or- 

 ganic nitrogen, and CaCOs found by chemical analysis, 

 as given in table 9. The CaCOs contents and other con- 

 stituents of these samples probably serve only to dilute 

 the colors produced by the hydrated oxides of manganese 

 and iron. 



In the northeast Pacific the colors of the red clays, 

 as well as their other physical and chemical characters, 

 show very little variation. Samples 69 and 72 are the 

 reddest and darkest of the moist samples, their color 

 .designations being 162k and 17m, respectively; whereas 

 sample 76 (173k, olive brown) is the lightest and grayest. 

 Five of the seven moist samples examined have colors 

 between 17l/2m and 173k, a range of only two shades 

 and 1I/2 increments of neutral gray. 



Samples 57 to 60, which are siliceous oozes collect- 

 ed in the region northeast of Japan, are similar in color 

 to the red clays of the northeast Pacific, as are samples 

 79 and 80, radiolarian oozes from the central Pacific. 

 Most of the representatives of terrigenous deposits in 

 the collection, namely samples 10, 32, 33, 34, 51, 55, 56, 

 61, and 63, are a slightly greenish gray in color, rang- 

 ing between 192l and 2l4b for moist samples. The re- 

 maining three terrigenous samples, 11, 53, and 54, are 

 brown in color, but are nevertheless designated as ter- 

 rigenous because of their high content of volcanic mate- 

 rials. 



Physical Characteristics 



Besides a designation for color, column 7 of table 1 

 also contains a description of the physical characteris- 

 tics of the samples, that is, of their texture, structure, 

 and consistency. The structure and consistency were 

 determined by examining a representative part of each 

 sample on a knife blade or in the hand. They are ex- 

 pressed in terms of certain standard expressions sug- 

 gested by the descriptions of the Challenger samples, and 

 follow, in part, the definitions given by Shaw (1927) for 

 the physical characteristics of soils. The textural de- 

 signations are of two types: (1) those based on the feel 

 of a sample when rubbed between the fingers, together 

 with its macroscopic appearance, and (2) the textural 

 classes of the system used by the United States Bureau 

 of Soils, given only when mechanical analyses are avail- 

 able. It was found impossible to express the textures of 



many of the samples in terms of Wentworth's (1922) 

 size classification. On the other hand, since the great 

 majority of deep-sea sediments contain more than 30 

 per cent of particles less than 5 microns in diameter, 

 and therefore must be classified as clays in the Bureau 

 of Soils' system, this classification often does not serve 

 to distinguish between different types of samples. It 

 does have the advantage of being quantitative, whereas 

 the terms based on the appearance and feel of the sam- 

 ples are only qualitative and subjective. The samples 

 have been divided on this latter basis into gravels, sands, 

 silts, and clays. When, as often happens, particles of 

 two different sizes are present in appreciable amounts, 

 the adjectival terms sandy, silty, and clayey have been 

 used. Most Globigerina oozes, for example, are sandy 

 clays or clayey sands. 



When macroscopic grains are present in noticeable 

 amounts, the shape and nature of the grains have been 

 given. If rocks or mineral fragments are present, the 

 grains are described as angular, subangular, subround- 

 ed, or rounded; similarly, the varying amounts and sizes 

 of macroscopic shells of foraminifera and other organ- 

 isms, and of clayey aggregates and manganese grains 

 and nodules have been noted. 



The structure, that is, the arrangement of the indi- 

 vidual grains and aggregates making up the sample, and 

 the consistency, that is, the degree of cohesion of the 

 material and the resistance opposed to forces tending to 

 deform or rupture aggregates, will obviously depend on 

 the amount of moisture in the samples. Corresponding- 

 ly, the descriptive terms used to express these charac- 

 teristics vary somewhat according to whether the sam- 

 ple was dry, moist, or wet when examined. For both 

 wet and dry samples, however, the terms coherent , mod - 

 erately coherent , slightly coherent, and incoherent 

 were employed; the first meaning that the individual 

 grains and aggregates have a high degree of cohesion, 

 and the last that the individual grains and aggregates do 

 not adhere to each other at all. For moist and wet sam- 

 ples the terms plastic, sticky , slippery ( greasy ), gran- 

 ular, and gritty, together with modifying adverbs, were 

 employed, and for dry samples the terms brittle, pul - 

 verulent, crumbly , and gritty were used. These terms 

 may be defined as follows: (1) plastic was used in the 

 sense given by Mellor (1922), "plasticity is the proper- 

 ty which enables a clay to change its shape without 

 cracking when it is sulsjected to a deforming stress;" 

 (2) sticky is defined by Mellor as follows; "a sticky clay 

 is one in which the particles do not have a marked ten- 

 dency to adhere together. Such clay adheres to anything 

 it touches which water can wet;" (3) slippery and 

 greasy were used to mean simply that a sample felt unc- 

 tuous or greasy to the touch; (4) a brittle soil is defined 

 by Shaw (1927) as one which "when dry will break with 

 a sharp clean fracture. If struck a sharp blow it will 

 shatter into cleanly broken hard fragments;" (5) crum - 

 bly is used to describe dry samples that break up easily 

 into soft, irregular "earthy aggregates;" (6) pulverulen t 

 is used in the sense of Murray and Renard (1891), that 

 is, to describe a dry substance which easily crumbles 

 to an impalpable powder. The above terms are all pro- 

 perties of the amount and kind of the clayey materials in 

 the sediments. For samples containing larger particles 

 or aggregates the terms g ritty , implying the presence of 

 a noticeable amount of angular hard grains, and g ranu - 

 lar, implying the presence of smooth aggregates or 

 rounded grains (as determined by the feel), were used. 



