Studies on water movements and sediments in Southern Lake Michigan : part 1[-3] ... / by John C. Ayers.

is a combination of the observations carried out on board ship,
when the sample was fresh, and re-examination of the material in
the laboratory under a binocular microscope with a metric scale
in the field of view. The term is used as an opposite to any of
the several means of designating sediment type by the measured
proportions of sand, silt, and clay determined in particle-size
analyses.
Each sample has been placed subjectively in a sediment-type
category on the basis of the field description of the uppermost
sediment layer, even if it was only a thin surface layer.
The sediment-type categories used follow the triangulargraph categorization of Shepard (1954) except that a subjective
basis rather than a percentage-composition basis is used. "Loam"
in the center of the triangle represents the several 3-way combinations of sand, silt and clay (sandy silty clay, clayey sandy
silt, silty clayey sand, etc.).
The use of only the uppermost sediment layer was dictated by
the fact that sediment-type changes resulting from eutrophication
will first be evident in the thin surficial layers.
The use of the field description of sediment type was necessary for three reasons: 1) eutrophication-caused changes will
probably be first visible as significant color changes in the
surface layer as it modifies toward the organic sediments (if not
between Hough's survey and this, then between this and some
future survey), 2) the presence of unnatural odors is detected
most surely in the field observation of the fresh sediment, and
3) sufficient funds for the scraping-off and analysis of samples
of the uppermost sediment layer were not available.

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