"Do you know what a fault is? Of course not! Or a horst? Ditto! Oh, a geology-lesson at Dieppe college was so many hours wasted! Well, lend me your ears, young Dubosc! I will be brief and to the point. The terrestrial rind--that is, the crust which surrounds the internal fire-ball, of solidified elements and eruptive or sedimentary rocks--consists throughout of layers superposed like the pages of a book. Imagine forces of some kind, acting laterally, to compress those layers. There will be corrugations, sometimes actual fractures, the two sides of which, sliding one against the other, will be either raised or depressed. Faults is the name which we give to the fractures that penetrate the terrestrial shell and separate two masses of rock, one of which slides over the plane of fracture. The fault, therefore, reveals an edge, a lower lip produced by the subsidence of the soil, and an upper lip produced by an elevation. Now it happens that suddenly, after thousands and thousands of years, this upper lip, under the action of irresistible tangential forces, will rise, shoot upwards, and form considerable outthrows, to which we give the name of horsts. This is what has just taken place. . . . There exists in France, marked on the geological charts, a fault known as the Rouen fault, which is an important dislocation of the Paris basin. Parallel to the corrugations of the soil, which have wrinkled the cretaceous and tertiary deposits in this region from north-east to north-west, it runs from Versailles to seventy-five miles beyond Rouen. At Maromme, we lose it. But I, Simon, have found it again in the quarries above Longueville and also not far from Dieppe. And lastly I have found it . . . where do you think? In England, at Eastbourne, between Hastings and Newhaven! Same composition, same disposition. There was no question of a mistake. It ran from France to England! It ran under the Channel. . . . Ah, how I have studied it, my fault, Old Sandstone's fault, as I used to call it! How I have sounded it, deciphered its meanings, questioned it, analysed it! And then, suddenly in 1912, some seismic shocks affected the table-lands of the Seine-Inférieure and the Somme and acted in an abnormal manner as I was able to prove--on the tides! Shocks in Normandy! In the Somme! Right out at sea! Do you grasp the strangeness of such a phenomenon and how, on the other hand, it acquired a significant value from the very fact that it took place along a fault? Might we not suppose that there were stresses along this fault, that captive forces were seeking to escape through the earth's crust and attacking the points of least resistance, which happened to lie precisely along the lines of the faults? . . . You may call it an improbable theory. Perhaps so; but at any rate it seemed worth verifying. And I did verify it. I made diving-experiments within sight of the French coast. At my fourth descent, in the Ridin de