THE OCEAN AND ITS WORK 



229 



X. p 





Present Sea /ei>eZ ^^ 



:>> Blue GroHo\*:.'v. ;*•.'•: :■: 



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. 



Ancient );.'•'.' .- 

 Sea Cave /;:•;'; 



/4/7C/'efff~ Sect /ei/e/ 









The Island of Capri, off the coast of Italy, offers an unusual ex- 

 ample of submergence within historic times (Fig. 222). In ancient 

 times a sea cave, now known as the Blue Grotto, was used by the 

 Romans as a resort from the oppressive heat of certain seasons. In 

 order to obtain light 

 an opening was cut 

 in the roof. Since 

 that time the land 

 has sunk so that 

 even the artificial 

 opening is now partly 

 submerged. The 

 blue color of the 

 grotto is due to the 



refraction of the sun's 



fiG. 222. — Section or the Blue Lrrotto, Island or 



rays in the water, by C apri, showing proof of subsidence. (Modified after 

 means of which the Von Knebel.) 

 red rays are lost. 



In some of the caves of the Bermuda Islands (Fig. 223), stalactites 

 hang from the roof and extend into the sea water which partially fills 

 the caves. Stalactites obviously could not have been formed in water 

 and therefore prove the former greater elevation of the island. 



The temple of Jupi- 

 ter Serapis at Poz- 

 zuoli, near Naples, 

 proves that the coast 

 has suffered, first an 

 elevation, then a de- 

 pression, and finally 

 a reelevation almost 

 to its former level. 

 The evidence is to be 

 found in three col- 

 umns of the temple, 

 whose surfaces have 

 been roughened for 

 a height of from 12 to 21 feet above the base by boring mollusks 

 (Lithodomus) which live only in sea water. The temple was, of 

 course, built on land. It was then submerged by the sinking of 

 the coast, so that the columns were immersed in the sea to a height 



Fig. 223. — Diagrammatic section through a cave in 

 the Bermuda Islands, showing one proof that subsidence 

 has taken place. Stalagmites and stalactites are formed 

 only in the air. 



