LAND AND WATER 37 



without giving us any information as to their nature or their 

 temperature. Under such colossal pressure probably the heat 

 can no longer affect the mobility of the molecules : all bodies 

 must appear rigid and solid. The distinctions made on the 

 earth's surface between the various states of bodies no longer 

 have any significance in these central regions. 



However that may be, if the internal heat makes itself 

 so little felt on the earth's surface to-day, we may perhaps also 

 assume that it had very little influence during the epoch in 

 which the first consolidated layer could support sediments 

 more than 20,000 metres thick, as was already the case at the 

 beginning of the primary period, not long before the first 

 appearance of life. From that time onward climates have been 

 determined by action from without the earth, and this action 

 can only have been that of the sun — whose intervention we 

 must now study. 



