We regard an earthquake, as we see it, as a destructive force. That is because it destroys the works of man. But earthquakes are doing constructive work as well; or, at any rate, they are usually present when constructive work is being done. Destructive forces, such as erosion, are wearing down the structure of the globe, while earthquakes are the only known forces that are building it up. It is true that when an earthquake occurs rocks often fall, loose sediment is shaken down, and other settlements occur, but the real constructive work consists in upheavals, little by little, as it may be, of beaches, islands, coasts, plateaux, and perhaps larger areas. These elevations are actually witnessed in certain earthquakes. Many islands in the sea have been raised from time to time within even living memory. The south-western part of the island of Crete has been elevated within the historical period. The region about Pozzuoli and the Bay of Naples has suffered both elevation and depression. There is the famous instance cited by Sir Charles Lyell nearly eighty years ago of the Temple of Jupiter Serapis. This temple had many columns; and they are now situated on dry land. The pillars are forty-two feet in height, and for twelve feet upwards they are of smooth undisfigured marble. Then for another twelve feet they are pitted with the holes made by a marine shell-fish called _Lithodomus_, the stone-dweller. What are we to judge from this? The temple was first built on dry land. Then the land sank taking the temple with it, and the columns were submerged in sea sediment to a depth of some thirty feet above their pedestals. The lower portions of these pedestals were preserved intact, but the marine shell-fish found a home in the upper part of the marble columns, and pierced them with the channels and grooves. After this had gone on for a number of years the elevation of the land lifted the temple and its columns clean out of the sea again, and the marine shell-fish could no longer live in the columns. But the traces of their habitation remain. The elevation of this coast was actually witnessed at the time of the eruption of Monte Nuovo in 1538. Moreover, the raising of the land was perceived on a larger scale round the whole of the Bay of Naples during the eruption of Vesuvius in April, 1706. Professor Lorenzo found the elevation of the land at Pozzuoli to be six inches, and at Portici one foot.[14] The foundations of both Etna and Vesuvius were ages ago laid in the sea. [Footnote 14: The coast about Pozzuoli is now sinking again.]