In a paper on the Red Chalk, which I had the honour to address to your Society last year, I said, with reference to the surface configuration of the Wolds, that the rim or highest portion of the basin of the chalk area was now thinnest “owing to subaerial denudation.” These latter words have been objected to by a friendly critic, who says that I ought to have written “owing to submarine denudation.” This criticism opens at once the floodgates of controversy. Different men, equally distinguished as geologists, hold different opinions on the subject of denudation. Let me first explain my meaning in the quotation alluded to. All that I meant to assert was, that after the final emergence of the chalk area of the East Riding above the sea level, that portion of it which constitutes the high Wolds was exposed to subaerial denudation, and therefore reduced in thickness and made so far thinner in comparison with the other portion, which is protected from atmospheric influences by the Boulder Clay of Holderness (see Appendix A). I did not mean that in the process of elevation no other causes had tended to produce the thinness of the rim itself, which is only 200 feet on the highest ground, as compared with 800 feet below the clays of Holderness (see Appendix B). Nor did I intend to convey the impression that the present configuration of the Wolds, with its remarkable ramification of deep sinuous dales, was owing solely to subaerial denudation.