In a recent number of the American Journal of Science* President Chamberlin and myself discussed at some length the relationship of certain gravels in the middle Mississippi basin to the loess and to such other formations of that region as were demonstrably of Pleistocene age. In that article we expressed the conclusion that the gravels in question, composed mainly of chert and of other silicious impurities from limestone, were of pre-Pleistocene age. The evidence on which this conclusion was based need not here be repeated. We then believed it adequate to the conclusion reached, and nothing has subsequently been discovered by us to weaken the force of the arguments then used or to alter the conclusions based upon them.
Since the discussion referred to was published, some additional facts have come to light which have an important bearing on the . . .