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In a stratigraphic study of the sediments in and about Sodon Lake, Oakland County, Michigan, Cain and Slater (Ms.) examined 10 profiles from a transect line tangent at its mid point to the lake shore and about 20 feet from the water's edge at the closest (mid) point. A boring made at this point is designated Profile I; the materials of this boring were selected for pollen analysis. An additional transect of four profiles lies along a radius of the lake and intersects the former transect at right angles at the site of Profile I. The boring tool (modified Hillier peat sampler) was so calibrated that samples were obtained in pairs separated bv 6inch intervals, each sample being obtained about 3 inches distant from the respective ends of the opening of the tool. Each saml)le consisted of 5-10 cc. of sediment. and was placed immediately into a plastic vial. The vials were stored in a refrigerator until slides could be prepared for )ollen analysis by the Erdtman acetolysis method, modified by use of fresh rather than (lriedc material. The samples were then dried for purposes of standard color description and other types. of analysis, Cain and Slater (MAils.). The profiles were located on the west side of the lake where they transacted certain aquatic zones, herbaceous and shrub fens, and various types of swamp forest. The present-day vegetation of the lake has been described by Cain and Slater ('48). As would be expected from the position of Profile I. in the presentday herb-shrub fen, the first several feet of the sediments were composed of subaerial peat. At the 8-ft. level the sediments changed predominantly to marl, which was continued to the 23-ft. level except for two interruptions. Starting at 14 feet, there was a peat layer of about 9 inches thickness. Just above the 21ft. level was a second, but thinner, peat layer. Below the marl, between 23 and 23.5 feet was a sandy layer, under which was a slightly bluish clay layer of which we could obtain only a 6-in. sample. Since our tool was incapable of penetrating any deeper into these stiff sediments, the columni has a total thickness of 24 feet, and is analyzed on a basis of samples from 6-in. levels. Two slides of the acetolvzed material were prepared for each level. This was usually a superabundance of material, but in some cases additional slides were prepared so as to obtain adequate numbers of pollen grains. At a few levels we were unable to obtain as many as 200 pollen grains of trees, although the total number employed in the spectra was never less than 146 and the average was well over 200 grains. At two levels (1.5 and 2.5 feet) the peat apparently does not contain many microfossils, for repeated attempts failed to yield any pollen. The material was saffranin stained and mounted in glycerine jelly. Examination was made at a magnification of 440 x with a compound binocular scope and a mechanical stage. After the 49 spectra had been computed, the slides were reexamined for size-frequency studies of spruce (Cain, '48) and pine pollen (Cain and Cain, '48), and for non-tree pollen anud spores such as Sphagnum. Nliiluar, grasses, sedges, Lycopodium, etc. Since the identification of pollen grains andl their proportions in the various spectra are so critical for the interpretation of vegetational and climatic history by pollen analysis, one always wonders about the reliability of particular results. Some |
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