On several occasions I have been asked wh ether topics of earth science could be explained in more or less conventional prose. Of course this can be done. I ho pe chapter I meets with the most extreme wishes in this respect. I even venture to believe that chapters II, IV, VI and VII can also be digested without special strain. Though chapter V, and parts of chapter III may require a special effort of concentration on the part of the reader, there should be nothing in this book that cannot be under stood by an intelligent person who is willing to try. Sometimes, however, the use of technical...