In some recent papers published in the geological magazine, I have endeavoured to show that at the close of the Mammoth age there was a very considerable dislocation of the earth's crust, and that a consequence of it was the upheaval of some of the highest masses of land on the earth, including the massive mountains of Asia and the American Cordillera. I now propose to show that (as is à priori probable) there was a concurrent collapse or sinking of the ground over large areas, which, as in the corresponding upheaval, was very rapid, if not sudden.