CONSOLIDATION OP THE EARTH 9 



pleted soon after the birth of the moon. The temperature 

 of its surface at the time of consolidation was about 

 1,200C., and it was, therefore, still surrounded by its 

 primitive deep atmosphere of steam and other gases. 

 This was the second critical period in the history of the 

 earth, the stage of the " consistentior status," the date of 

 which Lord Kelvin would rather know than that of the 

 Norman Conquest, though he thinks it lies between 

 twenty and forty millions of years ago, probably nearer 

 twenty than forty. 



Now that the crust was solid there was less reason why 

 movements of the atmosphere should be unsteady, and 

 definite regions of high and low pressure might have been 

 established. Under the high-pressure areas the surface 

 of the crust would be depressed ; correspondingly under 

 the low-pressure areas it would be raised ; and thus from 

 the first the surface of the solid earth might be dimpled 

 and embossed.* 



The cooling of the earth would continuously progress, 

 till the temperature of the surface fell to 370 C., when 

 that part of the atmosphere which consisted of steam would 

 begin to liquefy ; then the dimples on the surface would 

 soon become filled with superheated water, and the pools 

 so formed would expand and deepen, till they formed the 

 oceans. This is the third critical stage in the history 

 of the earth, dating, according to Professor Joly, from 

 between eighty and ninety millions of years ago. With 

 the growth of the oceans the distinction between land and 

 sea arose in what precise manner we may proceed to 

 inquire. If we revert to the period of the " consistentior 

 status," when the earth had just solidified, we shall find, 



* It would be difficult to discuss with sufficient brevity the probable 

 distribution of these inequalities, but it may be pointed out that the 

 moon is possibly responsible, and that in more ways than one, for 

 much of the existing geographical asymmetry. 



