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 sige 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: 
Firstly, 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’ 
