256 



THE EARTH'S CRUST 



The folding and warping of the rock layers, as shown by 

 the picture on page 249, has brought some of the stratified 

 beds which were originally horizontal into an almost verti- 

 cal position, so that we now find at the surface the worn-off 

 edges of these beds. The different kinds of rocks and the 



different positions in 

 which the rock layers 

 are presented to the 

 forces which are active 



lite in wearing them away 



Ek Hj cause great variety in 



the forms of the sur- 

 face features. 



STRATIFIED ROCK 



These layers have remained horizontal as 

 originally formed. 



Continental Shelf. 

 Around the border 

 of the continents and 

 of those islands which 

 are near the conti- 

 nents, there extends, 



in some cases to a distance of two or three hundred miles, 

 a gradually deepening ocean floor. This gradually deep- 

 ening border is* called the continental shelf. When this 

 floor has reached the depth of about 600 feet, the gradual 

 slant suddenly changes into a quick descent to the depths 

 of the ocean, two or three miles. 



Upon such shelves lie the great continental islands, like 

 the British Isles and the East Indies. Continental shelves 

 furnish the great fishing banks of the earth, such as the 

 Grand Banks of Newfoundland and those around Iceland 

 and the Lofoten Islands, where fishermen for ages have 

 obtained vast supplies of fish. There is no equal area of 



