Fig. 285.—View of the three standing columns of the temple of Jupiter Serapis at Pozzuoli, showing the dark and rough band nine feet in width affected by the rock-boring mollusks which now live in the Bay of Naples.
In the ruins of the ancient temple of Jupiter Serapis are three marble monoliths 40 feet in height, curiously marked by a roughened surface between the heights of 12 and 21 feet above their pedestals ([Fig. 285]). Closer inspection shows that this roughened surface has been produced by a marine, rock-boring mollusk, the lithodomus, which lives in the waters of the Bay of Naples, and the shells of this animal are still to be found within the cavities upon the surface of the columns. Without recounting details which have been many times recited since these interesting monuments were first geologically explored by Babbage and Lyell, it may be stated that a record is here preserved, first of subsidence amounting to some 40 feet, and of subsequent elevation, of the low coast land on which stood the temple in the old Roman city of Puteoli ([Fig. 286]).
At the time of deepest submergence the top of the lithodomus zone upon the column stood at the level of the water in the Bay of Naples, the smoother lower zone being buried at the time in the sand at the bottom, and thus made inaccessible for the lithodomi. It is to be added that studies made in the environs of Pozzuoli have fully confirmed the changes of level revealed by the columns, through the discovery of now elevated shore lines which are referable to the period of deep submergence.
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.
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.
