DR. E. B. BAILEY, director of the Geological Survey of Great Britain, gave a Friday discourse on November 3 at the Royal Institution on "Mountains that have Travelled Over Volcanoes". Many mountain chains present a complexity of internal structure which recalls, with great magnification, that of pack ice piled sheet upon sheet by a tempest of yesterday. In 1893 it was realized by geologists studying the Alps that a far-travelled thrust-sheet may often be distinguished by the foreign characteristics of its constituent geological formations, just as clearly as a far-travelled man by the foreign characteristics of his face and dress. The Kiogar mountains on the borders of Tibet and India illustrate this phenomenon to perfection. The rock formations making the summits have very special characters spoken of collectively as Tibetan. The underlying formations making the lower slopes are shown by their fossils to be of the same geological age as the Tibetan formations overhead; but they have much more familiar characters spoken of collectively as Himalayan. Between the Tibetan and the Himalayan developments lies a thick separating complex layer of igneous rocks. Some of these igneous rocks are submarine lavas, following in normal succession upon the underlying Himalayan sediments. Some, however, exhibit intrusive relations and penetrate the overlying Tibetan sediments. The conclusion is reached that in the days before the upheaval of the local sea bottom to give the Himalayan mountains, an invading thrust-sheet penetrated the area from the north. On its way it passed over a group of submarine volcanoes, which, driven underground, maintained a guerilla attack by injection of molten material from below. Wear and tear due to withdrawal of over-run, overloaded mobile sediments added to the general confusion.