Evidence is gradually accumulating that the presently accepted (Holmes-Marble) geologic time scale should be lengthened, and that this extension should be greatest in the Paleozoic era. Age determinations on glauconites, however, contradict this evidence and generally support the present scale. A review of available data indicates many uncertainties. It still seems doubtful to attempt the construction of a new time scale until the key points can be established firmly enough to be useful.

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