254 



EARTH FEATURES AND THEIR MEANING 



possible to date more or less definitely the periods of subsidence 

 or elevation. At the little town of Pozzuoli, upon the shore of 

 the Bay of Naples, is found one of the most instructive of these 

 records. 



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 rough- 

 ened 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 



FIG 285. -View of the three standing Q the gurface of the columns> 



columns of the temple of Jupiter Se- ___. . . ,.,,., 



rapis at Pozzuoli, showing the dark Without recounting details which 

 and rough band nine feet in width have been many times recited 



affected by the rock-boring mollusks gince thege interesting monu . 

 which now live in the Bay of Naples. . 



ments were first geologically ex- 

 plored 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 re- 

 ferable 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 op- 

 posite directions, notwithstanding the fact that the general move- 

 ment of the province is one of uplift. Thus during the Alaskan 



