Figure 4: Se/Cu vs. redness graph. Both Se and Cu are measured in ppm whereas redness was measured with a spectrophotometer and is in lumens. Se is a trace element indicative of Lake Agassiz. Cu is more indicative of Lake Superior. Higher redness values indicate more of a true red color while lower numbers indicate more of a gray color. Most of the red field samples are clustering around the Lake Superior source material, but little correlation is seen between the gray field samples and the Lake Agassiz source material. (Johnson, 2009.)
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