248 CHAMBERLIN— THE AGE OF THE EARTH. 



not let them go as far as they proposed. The tandem was reined in 

 and marked time, losing not a little of the free natural pace it should 

 have retained. 



But in time this great antagonist was neatly flanked from an 

 unexpected quarter. Certain physicists and chemists discovered that 

 they had a decaying atom on hand. They keenly watched its rate of 

 decay and soon came to see that if atoms take as long to grow as 

 some of them take to die off, there should have been time enoueh for 

 this little ball of atoms to get together — and plenty of energy as well. 



So, too, astronomers began to see that the making of globular 

 clusters and stellar galaxies required time. If 60,000 suns have time 

 to come together and work themselves into a steady state while yet 

 they are suns, the getting together of our little earth may be merely 

 a negligible matter after all. And so a new order of things has 

 arisen. The tandem is a vexed tandem no longer. We now have a 

 fine four-horse team ; Astronomy and Physics at the front, leading 

 off at a great pace ; Biology on the pole, steadying the team, and 

 Geology plodding on as the old original wheel horse. 



The Geologic Problem. 



Now, I must hasten to warn you not to expect much of the old 

 wheel horse. He has grown stiff in his paces, and his paces are not 

 what they should have been. Kelvin checked him too high. A 

 reasonable check should have given him good form and some sense 

 of restraint, but checked too high, he took to short mincing steps. 

 As a result he's in poor shape to swing into the great pace of the new 

 leaders. It is too much to expect him to recover his natural step at 

 once, but he will in time. For the present, he will need a touch of 

 the whip now and then to make him keep pace. Let this be gentle 

 and considerate, because of his age and his past service, but let it 

 be persuasive. 



Representative Geologic Time-estimates. 



It is a simple matter, theoretically, to use the rate at which sedi- 

 ments are being laid down, or solutions gathered into the ocean, as a 

 divisor to find the time required to lay down the whole column of 

 sediments or the whole accumulation of the salts in the sea. Practi- 



