Professor Holmes's further article, substantiating points questioned by me, may be divided into two parts. In the first he gives a statement of some geological phenomena not yet explained in accordance with his old theory of the earth's thermal history. In the second he maintains that these demand the abandonment of the theory and its replacement by a new one, which I consider qalitatively wrong. With regard to the first part, I consider that Professor Holmes has done a great service to geophysics in bringing these points forward in so clear a way. It has never been claimed that the old theory explained everything, and in some points it certainly requires to be supplemented; the questions at issue are what modifications are required, and whether they are such as to change the whole character of the earth's thermal history. But before problems can be solved it is necessary that they should be stated, which is liable to be at least as difficult.