320 THE HISTORY OF OKEATION. 



since during the continued cooling, the fiery fluid nucleus 

 became more and more condensed and contracted, and 

 consequently the diameter of the earth diminished, the 

 thin cold crust, which could not closely follow the softer 

 nuclear mass, must have fallen in, in many places. An 

 empty space would have arisen between the two, had not 

 the pressure of the outer atmosphere forced down the 

 fragile crust towards the interior, breaking it in so doing. 

 Other unevennesses probably arose from the fact that, in 

 different parts, the cooled crust during the process of 

 refrigeration contracted also itself, and thus became fissured 

 with cracks and rents. The fiery fluid nucleus flowed up 

 to the external surface through these cracks, and again 

 became cooled and stiff". Thus, even at an early period there 

 arose many elevations and depressions, which were the fii^st 

 foundations of mountains and valleys. 



After the tempei^ature of the cooled terrestrial ball had 

 fallen to a certain degree, a very important new process was 

 effected, namely, the first origin of water. Water had until 

 then existed only in the form of steam in the atmosphere 

 surrounding the globe. The water could evidently not con- 

 dense into a state of fluid drops until the temperature of the 

 atmosphere had considerably decreased. Now, then, there 

 began a further transformation of the earth's crust by the force 

 of water. It continually fell in the form of rain, and in that 

 form washed down the elevations of the earth's crust, 

 filling the depressions with the mud carried along, and, by 

 depositing it in layers, it caused the extremely important 

 neptunic transformations of the earth's crust, which have 

 continued since then uninterruptedly, and which in our 

 next chapter we shall examine a little more closely. 



