HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Whittig, L. D. Articles by Cady, J. G. Search for Related Content PubMed Articles by Whittig, L. D. Articles by Cady, J. G. Agricola Articles by Whittig, L. D. Articles by Cady, J. G.

Characteristics and Genesis of Cascade and Powell Soils of Northwestern Oregon¹

ABSTRACT

Soils of the Cascade and Powell series of northwestern Oregon were studied to establish the identity of their parent materials, their mode of formation, and some of their physical and chemical properties. Conclusions were based upon integrated mechanical analysis, exchangeable cation, and mineralogical data coupled with field observation.

Common to each of the soils is one or more profile discontinuities marking zones of relatively recent deposition over pre-existing soil horizons. A similar and relatively high proportion of unweathered feldspar, hornblende, glass, and other such weatherable minerals is present in the sand fractions of the upper zones of each profile. Within the clay fractions, interstratified vermiculite-chlorite is a dominant constituent of these upper horizons and the ratio of expandable layer silicates to chlorite and the concentration of kaolin increases with depth. In both soils, relative concentrations of these clay minerals change abruptly between adjacent horizons. The abrupt differences in mineral concentrations are usually accompanied by a notable shift in particle size distribution and, in one case, by a marked difference in content of free iron oxide.

Each of the profiles contains a considerable amount of relatively unstable alumino-silicate clay material. As much as 20% of the clay fraction of some horizons is dissolved as SiO₂ and Al₂O₃ by digestion in 0.5N NaOH. Absence of gibbsite and lack of wide variation in ratio of dissolved SiO₂ to dissolved Al₂O₃ indicates the presence of allophane which has probably formed as a residue after leaching of bases from the volcanic glass present in the sand.

¹ Contribution from Soil Conservation Service, U.S.D.A. Presented before Div. V, Soil Science Society of America, Davis, Calif., Aug. 16, 1955.

² Soil Scientists, Soil Conservation Service, U.S.D.A., Beltsville, Md.

Received for publication March 16, 1956. Accepted for publication May 23, 1956.