In the discussion for which we have met today it is intended to summarize in a very general way the information now available on the subject which forms the title of this paper, to analyze that information and the deductions based on it, and to point the way for the achievement of more satisfactory results.
Geologic correlations are effected by the comparison of geologic phenomena or events revealed through geologic henomena in one region with geologic phenomena or events in another region in which the order of their succession in time has been standardized. Since geologic standards and comparisons with them constitute the basis of geologic correlations, the construction and utilization of such standards will be briefly summarized.
In stratigraphie geology the beginnings are found in single exposures or occurrences which may be concealed from view in their natural relations and are rendered . . .