DESCRIPTION OF SAMPLES 



43 



this strip underlies the average path of the Counter 

 Equatorial Current, which is known to have a high plank- 

 ton content, and the fact that the Carnegie found sili- 

 ceous Globigerina oozes to the south of the eastern part 

 of the area, make it seem reasonable to believe that this 

 zone of radiolarian ooze does exist as a continuous belt. 

 Small areas of radiolarian ooze lie to the south of the 

 Marianas, and near Maiden Island, and Schott also 

 shows several patches of radiolarian ooze in the 

 northeast Pacific, based on samples collected by the 

 Egeria . 



The presence of siliceous oozes on the bottom un- 

 derlying the area north of the north Pacific polar front, 

 first shown by Murray and Renard from a study of sam- 

 ples collected by the Tuscarora. was confirmed in part 

 by Carnegie samples 57 to 60. It should be noted that 

 sample 57 is a radiolarian ooze, whereas sample 58 con- 

 tains about equal proportions of radiolaria and diatoms. 

 In its eastern half this area is based on the map by Mur- 

 ray and Lee. The writer has pointed out already that 

 the diatomaceous deposits off the South American coast, 

 indicated by Schott as diatom ooze, should more proper- 

 ly be regarded as terrigenous diatom mud, a suggestion 

 which has also been made by Neaverson. 



The criteria for distinction between terrigenous and 

 pelagic deposits given in the section on classification 

 have resulted in a considerable extension of the zone of 

 terrigenous deposits off the coasts of North and South 

 America. It is probable that this zone would be even 

 further enlarged by a critical survey of the boundary 

 area. Similarly, in the northwest Pacific the zone of 

 terrigenous (volcanic) sediment shown on chart 2 is 

 somewhat larger than that indicated by Hanzawa. 



Calcium Carbonate Content 



The calcium carbonate contents of the samples were 

 determined in one of the three ways which are listed in 

 column 6 of table 1 as acid soluble CaO, total CO2, and 

 inspection. 



Partial chemical analyses were carried out on forty- 

 six of the samples and these included determinations of 

 the amounts of calcium and magnesium soluble in 10 per 

 cent hydrochloric acid. Brazier (1891) assumed that 

 the results obtained by such a procedure would give 

 rough determinations of the percentages of calcium and 

 magnesium carbonate in the samples, and on the basis of 

 this assumption he recorded the presence of considera- 

 ble amoimts of magnesium carbonate in deep-sea depos- 

 its, especially red clays. From this Hogbom (1894) was 

 led to conclude that enrichment of magnesium carbonate 

 is taking place in the deep sea. That Brazier's assump- 

 tion is untenable was pointed out by Harrison and Jukes 

 Brown (1895) and by Andree (1920). It will be shown 

 later that the Globigerina oozes contain practically no 

 magnesium carbonate. Determinations, however, car- 

 ried out by an absorption method, similar to that de- 

 scribed by Hillebrand and Lundell (1929), of the carbon 

 dioxide content of eight of the samples in which acid- 

 soluble calcium had also been determined (see table 12), 

 show that the latter determination is a rather accurate 

 measure of the amount of total carbonate in a bottom 

 sample. The results were accurate to about 1 per cent, 

 an error which is commensurate with those arising in 

 the course of the collection and preliminary handling of 

 the samples. 



Besides the eight analyses of total CO2 content just 

 mentioned, the total carbon dioxide content of fifteen 

 other samples was kindly determined by Harald Hammar 

 of the American Petroleum Institute. For most of these 

 twenty-three samples the basis of estimate of CaCOs is 

 listed in table 1 as total CO2. For the chemically ana- 

 lyzed samples in which determinations of the total CO2 

 were not carried out, the basis of estimate of carbonate 

 content is listed in table 1 as acid-soluble CaO. The re- 

 sults are reported to the nearest 1 per cent. 



The amounts of calcium carbonate in the remaining 

 samples, which were either too small in amount or for 

 other reasons were not quantitatively analyzed for cal- 

 cium, were roughly estimated by inspection. This pro- 

 cedure sometimes leads to large errors' when the sam- 

 ples are unusual in color or appearance, but often the 

 agreement between an estimate of CaCOs by inspection 

 and a subsequent quantitative determination is rather 

 close. Such estimates were carried out on the fifteen 

 samples later quantitatively determined by Hammar. 

 The average deviation between the estimates by inspec- 

 tion and the actual determinations was 10.6 per cent, but 

 this was chiefly caused by a large discrepancy of about 

 35 per cent in two samples. In eight of the fifteen sam- 

 ples the deviation was 3 per cent or less, and in twelve 

 of them the deviation was 12.5 per cent or less. Owing 

 to the magnitude of the errors involved, the estimates by 

 inspection are reported in table 1 to the nearest 5 per 

 cent. 



A comparison of the samples collected by the Chal - 

 lenger . Albatross , and other ships near the Carnegie 

 stations, as listed in column 10 of table 1, shows that in 

 general the carbonate contents given by Murray and his 

 co-workers are lower than those recorded in this paper 

 for the Carnegie samples. Murray's determinations of 

 CO2 v/ere carried out by the alkalimeter method, which 

 consists essentially of weighing a sample before and 

 after the displacement of carbon dioxide by dilute acid. 

 The samples were first dried in an air or water oven at 

 temperatures of 100° to 110°, but apparently they were 

 not washed free of salt. The Carnegie samples were 

 dried to constant weight at 110° or, in the case of the 

 samples analyzed by Hammar, were heated above 110°. 

 Examination of the section on chemical analyses given 

 below will show that the amounts of water in presumably 

 dry samples are quite variable in amount, depending on 

 the nature of the drying process. Most of the analyzed 

 Carnegie samples were washed partly free of salt. Since, 

 as Gebbing (1909) has shown, the salt content of fine- 

 grained sediments is sometimes as much as 7 per cent, 

 removal of the salt would cause a considerable increase 

 in calcium carbonate content. 



Color 



As stated already, the colors of the samples are in- 

 dicated in column 7 of table 1. Colors were determined 

 according to the scheme of color standards and nomen- 

 clature given by Ridgway (1912). In this system the 

 spectrum is divided into seventy-two hues which are 

 each designated by a number; 1 designates red, 16 half- 

 way between orange and yellow, 21 orange to yellowish- 

 yellow, and so on. The tint or shade, that is the amount 

 of white or black for any particular hue, is designated 

 by a letter. The seven letters a to g indicate progres- 

 sive increments of white, and h to n increments of black. 



