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Mineralogical Composition of Glacial Materials as a Factor in the Morphology and Genesis of Some Podzol, Gray Wooded, Gray-Brown Podzolic, and Humic-Gley Soils in Michigan¹

ABSTRACT

In this study the relatively unweathered glacial materials underlying 39 soil sites, representing 23 soil series, in Michigan were studied. The mineralogical compositions of the sand and silt fractions from those materials and some observations on the methods used in these determinations are reported here. The bulk densities, mechanical compositions, mineralogical compositions of the clay fractions, and acid soluble portions of each horizon of the soil profiles at these sites had been studied earlier. Some relationships of the mechanical to the mineralogical compositions of the glacial materials and their relations to the properties of the overlying soils are discussed.

As the number of particles per gram of the materials studied increased, the percentages of quartz decreased and the unidentified portion of the sample—chiefly in the clay fraction—increased. The mineralogical composition of the materials under different toposequences of soils indicated that in most cases field observations had correctly grouped mineralogically similar materials.

The calculated mechanical compositions and thicknesses of the sola that had apparently formed from materials similar to the glacial materials underlying them, were compared to those of their parent rocks, assuming that no net change had occurred in the mass of the acid insoluble portion. The sola had increased in thickness, except where the parent rocks contained more than 12% of acid soluble materials. In the latter cases, there had apparently been some collapse or shrinkage of the material associated with the removal of the soluble portion.

The net increases in clay contents of the sola of mineral soils in Michigan, compared to their parent rocks, are apparently small and decreases in clay contents are common, particularly in the Podzol—Gray Wooded (or Gray-Brown Podzolic) Intergrade or Humic-Gley profiles and the Gray Wooded or Gray-Brown Podzolic soils formed from fine-textured materials. The percentage increases in clay contents relative to that in the parent rocks are small except in very sandy materials where most of the clay, even though small in amount, may be pedogenic in origin.

¹ Contribution from the Soil Science Department, Michigan Agr. Exp. Sta., East Lansing, Michigan. Authorized for publication by the Director as Journal Article No. 1981 of the Michigan Agr. Exp. Sta. Presented before Div. V, Soil Science Society of America, Nov. 14, 1956, at Cincinnati, Ohio.

² Former graduate student at Michigan State University, now Assistant Professor of Soils, University of Kentucky, Lexington, Kentucky; and Professor of Soil Science and Associate Professor of Soil Science, Michigan State University, respectively.

Received for publication December 11, 1956. Accepted for publication March 12, 1957.