CHAPTER XI 



THE BED OF THE OCEANS 



251. The Lithosphere. The wide smooth expanse of 

 the hydrosphere is apt to give one a wrong idea of the 

 surface of the Earth by veiling the true topography of the 

 great hollows. Serious attempts to find out the whole 

 form of the lithosphere only began when the vast hidden 

 region acquired commercial value as a bed for telegraph 

 cables. Since the commencement of submarine telegraphy 

 accordingly the process of taking deep - sea soundings 

 ( 443) has been rapidly perfected, and hundreds of 

 accurate measurements of depth have been made in all the 

 oceans. During the magnificent expedition of the Chal- 

 lenger in. 1872-76, many deep soundings were taken for a 

 purely scientific purpose in parts of the oceans never likely 

 to be visited by telegraph ships. In recent years numerous 

 smaller expeditions fitted out by the British government 

 and by the governments of the United States, Norway, 

 Germany, France, and Austria -Hungary, have made de- 

 tailed studies of parts of the sea-bed. The form of the 

 floor of the ocean has thus been gradually felt out point by 

 point, and though quite in the dark as to the scenery of the 

 veiled part of the lithosphere, we are now able to compare 

 its general features with the smaller portion which is open 

 to the light of day. If the Earth, like the Moon, had lost 

 its hydrosphere, and could be viewed from a distance, the 

 surface would appear to be made up of two great and 

 roughly uniform regions, both convex, following the curva- 



