648 W. H. SHERZER RECOGNITION OF TYPES OF SAND GRAINS 



that described by Darton in New Mexico.^^ It is possible that it might 

 be locally accumulated into heaps of salt sand by wind action, although 

 this result would be resisted by the attraction that the salt has for 

 moisture. A similar occurrence of epsomite (magnesium sulphate) has 

 been noted in California by Major Emory/^ and that of mirabilite (so- 

 dium sulphate) by Talmage about Great Salt Lake, resulting from a 

 lowering of the temperature.^* It seems probable that granular deposits 

 might also be similarly formed of numerous other minerals, more or less 

 soluble in water, such as borax, alum, magnesite, chloromagnesite, thino- 

 lite, dolomite, aragonite, calcite, etcetera. ^^ 



To the extent that the deposition of calcareous tufa, travertine, and 

 silicious sinter results from the relief of pressure, loss of carbon dioxide, 

 cooling or evaporation, combined with the vegetable agencies enumerated, 

 we have a deposit of the organo-concentration subtype which might be of 

 granular texture or easily reducible to such. If there are oolites formed, 

 as described by Sorby,^^ by "the original deposition of calcite round 

 nuclei gently drifted along by currents of the ordinary temperature, 

 which caught up more or less of the surrounding mechanical impurities,'^ 

 such a result could be secured only in a concentrated, and hence over- 

 saturated, solution of calcium carbonate. Our classification would thus 

 separate the organically formed oolites from those due to over-saturation, 

 as it very obviously should do, providing there is this essential difference 

 in their mode of formation. The oolitic iron ore of the Clinton forma- 

 tion of New York is regarded by Smyth as not due to the replacement of 

 calcareous granules by iron oxide, but to the formation of original de- 

 posits of silica and oxide concentrically about rounded grains of quartz 

 as nuclei. This mode of origin, without the agency of vegetation, would 

 demand a certain degree of concentration of the solution furnishing the 

 materials. ^^ A silicious oolite from Center County, Penns3dvania, has 



52 Darton : Zuni saU deposits. BiUletin No. 260, U. S. Geological Survey, 1905, p. 

 565. See further, "Lake Bonneville," by Gilbert, Monograph I, U. S. Geological Sur- 

 vey, 1890, pp. 208 and 257, and "A description of the Salt Lake of Larnaca, In the 

 Island of Cyprus," by Bellamy. Quarterly .Tournal of the Geological Society of London, 

 vol. Ivi, 1900, p. 745. 



53 American Journal of Science, 2d ser., vol. vi, 1848, p. 389. 



s* Talmage : The waters of Great Salt Lake. Science, vol. xiv, 1889, p. 446. 



S5 An interesting discussion of the subject of chemical concentration will be found in 

 Russell's presidential address, prepared for the Geological Society of America in 1906, 

 "Concentration as a geological principle." Biilletin of the Geological Society of Amer- 

 ica, vol. 18, 1907, p. 12. See also his monograph on Lake Lahontan, U. S. Geological 

 Survey, No. xi, 1885, from p. 182, and following. 



^6 Proceedings of the Geological Society of London, vol. xxxv, 1879, p. 75 ; see also 

 "Mechanically formed limestones from .Tunagarh and other localities," by Evans, vol. 

 Ivi, 1900, p. 559. 



6'^ American Journal of Science, 3d ser., vol. xliii, 1892, p. 487. Reviewed in Ameri- 

 can Geologist, vol. x, 1892, p. 122. 



