- (A) = Total soluble in HCl.
- (B) = Corresponding to Bauxite.
- (C) = Other Soluble Matters.
- Miss. = Mississippi.
- Cal. = California.
| Number. | Name of Soil. | County. | State. | (A) | SiO₂ | Al₂O₃ | (B) | (C) |
|---|---|---|---|---|---|---|---|---|
| 195 | Prairie | Alcorn | Miss. | 28.57 | 3.6 | 14.4 | 14.12 | 2.92 |
| 346 | Dark Loam | Chicasaw | “ | 10.32 | 6.6 | 11.2 | 6.91 | .86 |
| 288 | Flatwoods Clay | Pontotoc | “ | 26.94 | 5.0 | 11.3 | 8.75 | 3.48 |
| 676 | Red Volcanic | Lake | Cal. | 41.00 | 5.9 | 22.6 | 21.90 | 2.00 |
| 332 | Mojave Desert | Kern | “ | 24.82 | 5.0 | 9.2 | 6.10 | 5.13 |
| 191 | Red Foothill | Merced | “ | 23.32 | 4.5 | 8.8 | 6.20 | 3.05 |
| 705 | Red Chaparral | Shasta | “ | 28.75 | 5.5 | 14.4 | 12.10 | 1.12 |
| 706 | ““ Subsoil | “ | “ | 28.40 | 4.7 | 17.4 | 16.70 | 1.32 |
| 573 | Tulare Plains | Tulare | “ | 29.27 | 3.4 | 8.7 | 7.20 | 11.16 |
| 701 | Dry Bog | “ | “ | 27.29 | 4.3 | 12.4 | 10.90 | 5.04 |
| 1004 | “Slickens“ Sed | Butte | “ | 30.80 | 8.0 | 14.2 | 9.20 | 1.95 |
| 656 | ““ | Yuba | “ | 22.23 | 3.0 | 10.4 | 9.80 | 2.19 |
| 517 | Brownish Loam | Butte | “ | 29.80 | 4.8 | 12.0 | 9.80 | 4.42 |
| 561 | Black Loam | “ | “ | 30.21 | 3.2 | 13.0 | 12.80 | 4.67 |
| 563 | Sacramento Alluvium | “ | “ | 23.46 | 2.7 | 10.4 | 10.90 | 4.58 |
| 863 | Red Foothill | Nevada | “ | 56.80 | 11.0 | 36.4 | 33.60 | 1.22 |
| 861 | ““ | “ | “ | 45.46 | 11.5 | 22.0 | 14.10 | 3.97 |
It is apparent from this table that if, as is probable, the aluminic hydrate accumulates in the “clay” of the analysis, it will in some cases form a very considerable percentage of the same, and detract to that extent from its plastic, adhesive and other properties. But it must be remembered that the assumption upon which this table is calculated, leaves out of consideration the zeolitic portion, which as the 6th column shows, is frequently quite large as measured by the bases found, to which no other form of combination can be assigned. Since some of the alumina undoubtedly takes part in the formation of such zeolites, the silica must to that extent be withdrawn from the estimate made for kaolinite. While it is impossible to make any definite numerical allowance for this fact, it clearly will tend in many cases to increase materially the amount of alumina that must be assigned to the hydrate condition. It will be noted that in most cases given, the alumina per cent is rather large.
The relatively large number of such cases shown in the table for California soils is not a matter of accident; for even a cursory glance at the columns of analyses of California (and Washington and Montana) soils, shows that the cases in which the alumina exceeds the silica in amount are rather predominant, while the reverse is the case in the humid region.[144] But it must not be inferred that the reverse relation is not also frequently observed even in the arid region; it occurs in fact in close proximity to the localities where some of the most striking instances of excess of alumina over soluble silica have been found.
Thus Nos. 861 and 863 from the neighborhood of Grass Valley, which show this excess most strikingly, occur within 15 miles of localities which show almost the reversal of the numbers given for the two former, and at a level of about a thousand feet lower. It would seem, on the whole, that the excess of alumina occurs most frequently in connection with soils formed from eruptive rocks; in the case referred to, from volcanic ash. It will require more detailed study to detect the causes of these marked differences.
Retention of Soluble Silica in Alkali Soils.—It is somewhat surprising that, contrary to the expectation one would naturally entertain, the alkali lands, so frequently rich in the carbonates of the alkalies that would dissolve free silica, on the contrary, show most frequently an excess of soluble silica over alumina. This is probably to be explained from the very liberal opportunities afforded in the alkali soils for the formation of complex zeolitic masses by the retention in soil of the soluble alkali salts, and the abundance of lime always present in them. As already stated, we usually find in alkali soils a very large proportion of both alkaline and earthy bases in acid-soluble silicate combinations. But much farther research is needed to explain fully the marked discrepancies observed in this respect between soils not only occurring in closely contiguous localities, but also showing marked similarities in their general composition.
Ferric Hydrate.—There is no obvious reason, from the chemical standpoint, why iron, that is, ferric hydrate or iron rust, should be more abundant in the soils of the arid regions, as the averages given in the table suggest; moreover, the fact does not impress itself upon the eye, since the orange or reddish tints are by far more common in the humid than in the arid regions of the United States at least. The California average is considerably influenced by the very highly ferruginous soils from the foothills of the Sierra Nevada, and by the black (magnetite) sand so commonly present; that of Oregon by the black, highly ferruginous country rock (basalts), from which they are partly derived. The average for Montana is not higher than that of three states of the humid region, and less than that of Kentucky. We might imagine a cause for depletion of iron in the soils of the humid areas in the frequency with which humid moisture and high temperature will during the summers concur toward the bringing about of a reducing process in the soil, which by getting the iron into proto-carbonate solution would make it liable to be leached into the subsoil, as is frequently the case; yet the resulting “black gravel” or bog ore, in its various forms, is of not infrequent occurrence in the arid regions also. A constant quantitative difference due to climatic conditions does not appear to be shown by the data thus far at command, but the finer distribution of the ferric hydrate in the humid temperate as well tropical regions is obvious to the observer, from the frequent redness of humid and tropical soils.
Manganese.—An unexpected and apparently well-defined contrary relation appears to be shown as regards the related metal manganese; the average percentage of which is in all cases less in the arid than in the humid region. The cause of this relation is altogether obscure; it is too frequent to be accidental.
Phosphoric Acid.—As regards that highly important soil ingredient, phosphoric acid, the indication in the table that there is no characteristic difference in the average contents in soils of the arid and humid regions, respectively, is doubtless correct. This substance is so tenaciously retained by all soils that there is no obvious reason why there should be any material influence exerted upon its quantity by leaching, or by any of the differences in the process of weathering that are known to exist between the two climatic regions. Moreover, it is apparent that the average for the arid region is made up out of very widely divergent figures; that of California exceptionally low (lower than any of those for the states of the humid regions), while those for Washington and Montana are exceptionally high. The latter is due to country rocks (“basalts”) showing abundance of microscopic crystals of apatite, which in some cases raise the contents of the soils in phosphoric acid to nearly twice the average given for the states.
The forecast that for most California soils, fertilization with phosphates is of exceptional importance, has already been abundantly confirmed by cultural experience. Few definite data are as yet available from other arid states, where fertilization is thus far sporadic and unsystematic. But it is predictable that in view of the presence of an excess of lime carbonate in the arid soils, and the unfavorable effect of this compound on the rapid solubility of tri-calcic phosphate demonstrated by Schloesing, Jr.,[145] by Böttcher and Kellner[146] and Nagaoka,[147] fertilization with readily available phosphate fertilizers will be found necessary among the first, all over the arid region, especially in view of the scarcity of humus in arid soils.