240 THE OCEAN 



suppose that when, through loss of heat, the 

 great deep-seated centrosphere suffers con- 

 traction, the outer lithosphere is adjusted to 

 the diminished volume through flow-changes 

 in the rocks of the tektosphere, this flow 

 being generally in the direction of the con- 

 tinental masses, the general tendency being 

 slowly to elevate the continental earth- 

 blocks and relatively to depress the sub- 

 oceanic earth-blocks. The rocky materials 

 of the tektosphere are probably more homo- 

 geneous than those of the overlying litho- 

 sphere, but not so homogeneous as the under- 

 lying more or less metallic centrosphere. 



The centrosphere. — It is generally admitted 

 that the earth as a whole is five and a half 

 times heavier than water, or about two and 

 a half times heavier than the materials of the 

 rocky crust — such as granite and limestone 

 — ^with which we are familiar. From this 

 it is inferred that the great massive core, or 

 centrosphere, is very largely composed of iron, 

 with gold, platinum, and other heavy metals. 

 This view is corroborated by the fact that the 

 molten lavas, protruded at the surface of the 

 globe and believed to have a very deep-seated 

 origin, are more basic in composition than 

 those regarded as having a more superficial 

 origin. Again, the ores of gold, silver, tin, 

 and other heavy metals, which are found in 



