=Simultaneous contrary movements upon a coast.=—In our study of the changes in the level of the ground that take place during earthquakes, it was learned that neighboring sections of the earth’s crust may be moved at different rates or even in opposite directions, notwithstanding the fact that the general movement of the province is one of uplift. Thus during the Alaskan earthquake of 1899, although portions of the coast line were elevated by as much as forty-seven feet, neighboring sections were raised by smaller amounts, and some small sections were sunk and so far submerged that the salt water and the beach sand were washed about the roots of forest trees.
[Illustration: FIG. 286.—Pozzuoli in the 3rd, 9th, and 20th Centuries.]
A region racked by heavy earthquakes, where the present configuration of the ground speaks strongly for a movement of somewhat similar nature, but with average movement of elevation much greater to the northward than in the opposite direction, is the extended coast line of Chili. This country is characterized by a great central north and south valley which separates the coast range from the high chain of the Cordilleras to the eastward. To the southward the floor of this valley descends, and has its continuance in the Gulf of Corcovado behind the island of Chiloe and the Chonos archipelago. The known recent uplift of the coast of Chili, particularly in the northern sections and during the earthquakes of the eighteenth, nineteenth, and twentieth centuries, lends great interest to this topographic peculiarity. Indications are not lacking that, during the earthquake of Concepcion in 1835, and of Valparaiso in 1907, the measure of uplift was greater to the north than it was to the south.
[Illustration: FIG. 287.—Map of San Clemente Island, California, showing the characteristic topography of recent uplift (after U. S. Coast and Geodetic Survey).]
=The contrasted islands of San Clemente and Santa Catalina.=—Perhaps the most striking example of simultaneous opposite movements observable in neighboring portions of the earth’s crust is furnished by the coast of southern California. The coast itself at San Pedro and the island of San Clemente, some fifty miles off this point, in common with most portions of the neighboring coast land, have been rising in interrupted movements from the sea, and offer in rare perfection the characteristic coast terraces (Fig. 287 and Fig. 278, p. 250). Midway between these two rising sections of the crust, and less than twenty-five miles distant from either, is the island of Santa Catalina, which has been sinking beneath the waves, and apparently at a similarly rapid rate (Fig. 288). The topography of the island shows the intricate detail of a maturely eroded surface, while that of the neighboring San Clemente shows only the widely spaced, deep cañons of the infantile stage of erosion (Fig. 165 and pl. 12 A). While Santa Catalina has been sinking, San Pedro Hill has risen 1240 feet, and San Clemente, 1500 feet. It is characteristic of a sinking coast line that the cliff recession is abnormally rapid, and evidence for this is furnished by the shores of Santa Catalina, upon which the waves are cutting the cliffs back into the beds of cañons, and so causing small falls to develop at the cañon mouths.