The most important phase of both geologic chronology and stratigraphy is the precision of correlation. Not only is this true, but precise correlation is the only scientific basis of the biological problems concerning the origin, dispersal, and distribution of faunas and floras and particular stocks. Moreover, since distribution and the paths of dispersal constitute the fundamental data of all paleogeographic studies, it is obvious that what might be called historical geology in the largest sense ultimately rests on the success with which correlations are made.
Many students in the past have discussed the criteria for correlation from varying points of view, and there have been numerous symposia before the Geological and Paleontological Societies in which particular problems of correlation have been discussed and in which the methods employed were exemplified.
I propose to refer but incidentally to some of these earlier discussions, nor is it necessary to attempt a . . .