THE GEOSPHERES 241 



veinstones of fissures and faults, are for many 

 reasons regarded as having largely originated 

 in gaseous emanations from very deep- 

 seated positions. Further, the meteorites 

 which fall on the earth from extra-terrestrial 

 spaces are for the most part made up of iron, 

 nickel, and the heavier metals, thus indicating, 

 as does also spectrum analysis, the pre- 

 dominant composition of celestial bodies. 

 The revolution of planets round their axes 

 and round the sun, the planes of their orbits 

 and the revolution of satellites around prima- 

 ries, are all remarkable features of the solar 

 system which point likewise to a common 

 origin of the bodies it contains. 



There are many reasons for regarding the 

 whole of the interior of the earth, beyond a 

 depth of thirty or thirty-five miles from the 

 surface, as having a very homogeneous com- 

 position and structure, whether we adopt the 

 nebular or the meteoric and planetesimal 

 hypothesis. If this great centrosphere be not 

 solid, it behaves at all events as if it were 

 as rigid as steel, and towards the centre, 

 being largely composed of iron, it has probably 

 a density of about 8. This view is sup- 

 ported by the manner in which earth- 

 quake vibrations are transmitted through 

 the great central mass of the earth. Tem- 

 perature observations in deep mines and 

 Q 



