THE GEOSPHERES 239 



earth-blocks apparently tend to become 

 elevated, whereas what information we have 

 about the floor of the ocean indicates that 

 there the similar earth-blocks tend on the 

 whole to subside. It is not likely that faults 

 and fissures extend deep into the lithosphere ; 

 they must be regarded rather as relatively 

 superficial phenomena. 



The tektosphere, — ^A great many recent 

 seismic, geodetic, gravity, and geological 

 researches go to confirm what had long been 

 indicated, that there is, at a depth of some- 

 where about thirty miles beneath the surface of 

 the earth, a more or less heterogeneous and 

 stony layer which, under varying conditions of 

 temperature and pressure, becomes solid, 

 viscous, or even liquid. It is to this layer, 

 interposed between the relatively cold, solid, 

 heterogeneous, acid lithosphere and the 

 highly heated, solid, relatively homogeneous, 

 basic and metallic centrosphere, that the 

 writer, a good many years ago, gave the name 

 of tektosphere. This plastic layer is believed to 

 be the region in which isostatic adjustment and 

 compensation take place, and it apparently lies 

 at a deeper level under the continents, com- 

 posed of lighter, more acid, and less fusible 

 materials, than under the ocean's floor, where 

 the rocky materials are apparently heavier, 

 more basic, and more fusible. We may 



