316 HISTORICAL GEOLOGY 



very oldest rocks we could hope to reach. For still another 

 contrast, we may turn to the future fate of the earth as 

 forecast by each of the opposing theories. If we follow the 

 older conception, we must predict a gradual cooling and final 

 refrigeration of the earth and even the sun, the absorption of 

 its dwindling atmosphere within itself, and the death of all 

 living creatures. Under the newer hypothesis, the outlook is 

 less gloomy. Looking ahead as far as imagination will safely 

 carry us, we can see no prospect of destructive changes. The 

 infinitesimally slow growth of the earth and its atmospheric 

 envelope should continue, and the evolution of living things 

 into higher and better kinds should have ample time for 

 accomplishment. 



QUESTIONS 



1. What prevents the planets from leaving the sun? 



2. If Jupiter should pass close to the earth, what would happen 

 to the moon ? Why ? 



3. If the Laplacian theory is correct, what materials should have 

 formed the first solid part of the earth? In what order should 

 other materials have been added ? 



4. If the planetesimal theory is correct, which would be brought 

 into operation first, weathering or wave action ? 



5. On the same hypothesis would the waters of the first seas 

 have been fresher or salter than in existing oceans ? Under the 

 Laplacian hypothesis ? 



6. On the Laplacian theory how should the volcanic activity of 

 early times compare with that of the present? 



7. One of the satellites of Mars revolves about the planet much 

 faster than Mars turns on its axis. How does this fact bear on the 

 Laplacian theory ? 



REFERENCES 



COMSTOCK : A Textbook of Astronomy. (New York, 1903.) 



MOULTON : An Introduction to Astronomy. (New York, 1906.) 



POOR : The Solar System. (New York, 1908.) 



TODD : A New Astronomy. (New York, 1897.) 



YOUNG : A Textbook of General Astronomy. (Boston, 1893.) 



