[11] Rivers of North America, p. 80.
[12] The correctness of Letheby’s analyses has been disputed, partly because of their disagreement with former analyses in the very high amount of lime, partly because of the high potash-content in the Low-Nile water. The lime content is, however, confirmed by the partial analyses made by Mathey in 1887, which gives an average of 44.1 for the year, while the older analyses, made in Europe, of transported water gave only half as much. Letheby working on the spot was doubtless more nearly right in this respect. His figure for potash in the “Low-Nile” water agrees with former determinations, but that in the “High-Nile” is approached only by that in the Dwina water. It may be suspected that the soda is too low and potash too high in this analysis.
[13] In some cases the soluble salts originate in rocks impregnated with salts from marine lagoons or landlocked lakes, or directly from their evaporation residues. But this is the exception rather than the rule.
[14] A zeolitic mass, at first gelatinous and then becoming granular-crystalline is frequently observed oozing from the lower surface of newly made concrete reservoir dams: just as we find similar oozes consolidated into natrolite crusts in the crevices of natural sandstones.
[15] T. M. Reade (in his treatise on Chemical Denudation in Relation to Geological Time) calculates that 143.5 tons of lime carbonate are annually removed by solution from each square mile of land in England and Wales, and that the average amount thus removed annually from each square mile of the earth’s surface is about fifty tons.
[16] Bull. No. 1, U. S. Dept. Agr. Veg. Path. and Physiol. Investig.
[17] This term was first employed by Th. Schloesing, in communications to the French Academy of Sciences, and reported in the Comptes Rendus of that body; first in 1870. Unaware of Schloesing’s work, the writer began a full investigation of the subject of mechanical soil analysis in 1871, and published the results in 1873 (Am. Jour. Sci., Oct. 1873). Up to that time the limited resources of the library of the University of Mississippi had not given him an opportunity to see Schloesing’s publication. The two independent investigations, though conducted on somewhat different lines, gave of course practically the same results, and complement each other.
[18] There is still some discussion as to the chemical identity of colloidal clay with Kaolinite; but the objections are not convincing.
[19] It has of late been attempted to extend the meaning of this word to the behavior of all powders when wetted with water. But the adhesive plasticity of clay stands almost alone, in that (aside from contraction) it preserves in drying the form into which it may have been molded while wet, even when struck, whereas other powdery substances similarly treated at once collapse back into the original powder. The exclusive use of clay in modeling offers the typical example of plasticity as generally understood. The addition of any powdery substance, however fine, diminishes the plasticity of clay.
[20] American Journal of Science, 2d Ser., Vol. 43, p. 357.