358 THE BEAUTIES OF NATURE CHAP. 



to coincide roughly with the greatest height 

 of the mountains. There are indeed cases 

 recorded in which it is said that "no bottom" 

 was found even at 39,000 feet. It is, how- 

 ever, by no means easy to sound at such great 

 depths, and it is now generally considered 

 that these earlier observations are untrust- 

 worthy. The greatest depth known in the 

 Atlantic is 3875 fathoms a little to the 

 north of the Virgin Islands, but the sound- 

 ings as yet made in the deeper parts of the 

 Ocean are few in number, and it is not to be 

 supposed that the greatest depth has yet been 

 ascertained. 



CORAL ISLANDS 



In many parts of the world the geography 

 itself has been modified by the enormous de- 

 velopment of animal life. Most islands fall 

 into one of three principal categories : 



Firstar, Those which are in reality a part 

 of the continent near which they lie, being 

 connected by comparatively shallow water, 

 and standing to the continent somewhat in 



