GENERAL INTRODUCTION 3 



land and where there is an absence of rivers to extend, 

 in a seaward direction, with their deposits such shallows 

 as have been formed by erosion through wave action. Such 

 regions are on the western coast of North Africa, and the 

 Californian coasts of America. The effect of rivers in 

 widening this shelf can be very clearly seen on the north 

 coast of Egypt where it stretches out for over forty miles 

 in the neighbourhood of the Nile mouths, while 100 miles west 

 of Alexandria the 100 fathom line is reached within five 

 miles. 



CONTINENTAL 

 EDGE 



SEIA SURFACE 



ABYSS 



Fio. I 



From the outer edge of the continental shelf starts the 

 Continental Slope which is generally taken as stretching 

 down to 900 or 1,000 fathoms. This slope is comparatively 

 steep and may be said to constitute the sides of the ocean 

 basins. Its upper limit, the 100 fathom line and outer edge 

 of the continental shelf, is sometimes known as the 

 Continental Edge. 



B 



