_ THE DEPTHS OF THE SEA 9 



no shallow water and in some places a person 



may stand on the shores and drop a line into 



a thousand fathoms or more of water. Where 



these islands are of volcanic formation they 



often contain active volcanic craters and are 



liable at any time to be partially submerged 



or to be suddenly raised many feet above their 



I present level. Indeed, a great many of them 



\ are constantly rising or falling, although the 



I motion may be so slow and gradual as to pass 



1 unnoticed. Wherever there is an active vol- 



1 jcano sudden and violent changes are liable to 



1 occur and we have ample proof that numerous 



/ volcanic islands have been repeatedly sub- 



^^Itif rged and then raised again for hundreds of 



feet during past ages. 



On some of the West Indian islands, for 

 example, one may find fossil coral-reefs, shells 

 and other forms of marine life, similar to those 

 which exist to-day, far up on the forest-covered 

 mountain-sides, proving that at some period 

 the land has been raised far above the level 

 that it occupied when the reefs were formed. 

 Moreover, in many cases these fossil corals 

 alternate with layers of lava and volcanic ash, 



