194 THE PHYSICAL FORMATION vP THE EARTH. 



axis at double its present speed (Adams). If the earth 

 consolidated at or before this time, its ellipticity ra.ust have 

 been at least ■^^■^, and therefore its solidification took place 

 at a considerably later date (Thomson). Darwin, however, 

 states that sub-aerial denudation renders this method of 

 estimation unreliable. From the law of cooling, 10,000,000 

 years has been calculated to bo the time elapsed since the 

 consolidation of the earth's surface (Thomson). Darwin 

 objects to this also, inasmuch as, according to him, tidal 

 friction will have generated sufficient heat to materially 

 augment the length of time taken by the earth to reach its 

 present temperature. 



