CHEMICAL ANALYSES 



57 



date and determined by the alkalimetric method. Total 

 iron oxide was determined on a separate portion by the 

 potentiometric method. In determining the acid soluble 

 calcium and magnesia, a separate portion was treated 

 with 10 per cent hydrochloric acid until effervescence 

 ceased. It was then filtered and the usual procedure fol- 

 lowed." 



Molecular Ratios 



Owing to the varying amounts of calcium carbonate, 

 sea salts, and water present in the samples, the most 

 satisfactory way of making comparisons between differ- 

 ent analyses and with the results of other workers on 

 fine-grained sediments and soils, is by calculationof the 

 molecular ratios between various constituents, namely, 

 the ratios of silica to the combined sesquioxides of iron 

 and alumina and to each one of these individually, the 

 ratios between the two sesquioxides themselves, the ra- 

 tios between silica and the total bases, the ratios of ses- 

 quioxides to total bases, and the ratios between the 

 bases. These ratios are given in table 10, and represent 

 values obtained after attempted elimination of calcium 

 carbonate, and of the bases present as soluble sea salts. 

 It may be seen that most of the samples analyzed can be 

 classified ^ the following groups corresponding to de- 

 posit types and location: (1) a group of ten clays from the 

 northeast Pacific, samples 61 to 77; (2) five siliceous 

 sediments collected northeast of Japan, samples 56 to 

 60; (3) five south Pacific clays, samples 31 to 35; (4) 

 a group of fourteen normal and ferruginous Globigerina 

 oozes from the southeast Pacific, samples 16 to 29, and 

 41 to 45; (5) four siliceous Globigerina oozes from the 

 southeast and central Pacific, samples 13, 14, 81, and 

 82; (6) two radiolarian oozes from the central Pacific, 

 samples 79 and 80. Average and extreme values of the 

 ratios for each one of these groups are given in table 11. 



The group of northeast Pacific clays is very uniform 

 in chemical composition, the extreme silica sesquioxide 

 ratios deviating by only 3 per cent from the average val- 

 ue of about 4.0. In these clays alumina is the principal 

 sesquioxide, there being nearly four times as much alu- 

 mina as ferric oxide. The ratio between silica and total 

 bases of approximately 7, though rather narrow, is close 

 to that of certain soils. The sum of the divalent bases is 

 greater than that of monovalent bases. Magnesium is 

 the principal divalent base, and the amount of potassium 

 is nearly twice that of sodium. 



Owing to the presence of acid volcanic glass, and of 

 colloidal hydrated silica in the skeletons of siliceous or- 

 ganisms, the average silica sesquioxide ratio of the sili- 

 ceous volcanic mud and more or less volcanic siliceous 

 oozes collected northeast of Japan is about 6, which is 

 considerably higher than in the northeast Pacific clays. 

 This ratio, however, is remarkably constant in view of 

 the marked differences, corresponding to distance 

 from shore, in the relative amounts of siliceous organ- 

 isms and volcanic debris in these samples. Sample 56, 

 for example, probably contains more than 50 per cent of 

 volcanic material, whereas sample 60 consists very 

 largely of the remains of siliceous organisms and clays. 

 It would seem logical to infer that silica leached out 

 during the process of subaerial or submarine weathering 

 of volcanic material, similar to that present in sample 

 56, has been utilized by marine organisms whose dead 

 skeletons, fallen to the bottom, have restored the silica 



to the deposits. Although sample 60 represents a pro- 

 found physical alteration of the original volcanic debris 

 present in sample 56, there has been only a small net 

 change in chemical composition. 



In these siliceous muds and oozes, as in the north- 

 east Pacific clays, the molecular amount of alumina is 

 about four times that of ferric oxide. There are twice 

 as many molecules of divalent as of monovalent bases; 

 sodium and potassium are present in about equal propor- 

 tions; there is more than twice as much magnesium as 

 calcium. 



The siliceous oozes from the central Pacific differ 

 in several respects from those from the northwest Pa- 

 cific. The silica sesquioxide ratio is again nearly 6, and 

 the molecular amount of alumina is about three times 

 that of ferric oxide; but the ratio of silica to total bases 

 is relatively very low. Calcium and magnesium make up 

 about two -thirds of the bases. There is more than twice 

 as much potassium as sodium and more than four times 

 as much magnesium as calcium. 



The three south Pacific clays selected for analysis 

 contain considerable amounts of siliceous organic re- 

 mains and this is reflected in the average silica sesqui- 

 oxide ratio of more than 5. There are again about four 

 times as many molecules of alumina as of ferric oxide; 

 the ratio of silica to total bases is somewhat wider than 

 in any other sediments analyzed, owing to the very low 

 magnesium content of sample 34. Calcium and magnesi- 

 um are present in only slightly greater amounts than so- 

 dium and potassium, and there is a slight excess of 

 potassium over sodium. There is about three times as 

 much magnesium as calcium in samples 31 and 35. 



In the group of normal and ferruginous Globigerina 

 oozes from the south Pacific the silica sesquioxide ratio 

 never exceeds 3.23 and in several cases is less than 1.5. 

 In other words, the noncalcareous parts of some of these 

 samples, far from being similar to red clays even of the 

 same region, are almost lateritic in composition. Three 

 possible explanations suggest themselves for the ob- 

 served composition of the noncalcareous material. (1) 

 It may be in part lateritic soil material, so characteris- 

 tic of the tropics, which has been carried in suspension 

 from land and deposited with the shells of pelagic fora- 

 minifera. That not all the material has originated in this 

 manner is shown from the fact that the red clays of this 

 same region do not have as low silica sesquioxide ratios 

 as the Globigerina oozes. (2) It may represent the resi- 

 due of submarine weathering of volcanic and other de- 

 posits under the alkaline conditions presumably present 

 in the CaCOs-saturated interstitial water of the Globig- 

 erina ooze. (3) The alkaline condition referred to may 

 have been favorable especially for the precipitation from 

 solution or colloidal suspension of ferric and manganese 

 oxides, and to some extent of free alumina. It is note- 

 worthy that the molecular amount of iron oxide is about 

 three times that of alumina. The calculation of the silica- 

 base ratios and the ratios of divalent to monovalent bases 

 could not be carried out successfully, owing to the diffi- 

 culty of eliminating all the carbonate calcium. It may be 

 seen, however, that the average ratio of sodium to po- 

 tassium is about unity. Magnesium probably makes up 

 at least two-fifths of the total divalent bases. 



The average silica sesquioxide ratio of the four sili- 

 ceous Globigerina oozes which were analyzed, is very 

 high. Alumina is the principal sesquioxide present; so- 

 dium and potassium are present in about equal amounts; 

 at least two-fifths of the total divalent bases after 



