X907 ] AND CONTRACTION OF THE EARTH. 203 



may not be explained by ordinary earthquakes. The preservation 

 of the ruins of temples of the classic period alone assures us that 

 no really deep-seated convulsion of the earth has occurred within 

 the last 2,000 or 3,000 years. This general fact seems therefore 

 decidedly adverse to the doctrine of deep-seated movements of the 

 globe. 



To be entirely confident, however, that such cataclysms may not 

 occur at very long intervals, it is necessary to consider the indica- 

 tions furnished by the ruins wrought by geological time. The exist- 

 ence of a vast number of more or less unstable natural pinnacles, in 

 the form of columns of weather- and water-worn rock, scattered 

 abundantly in various parts of the earth, all of an age to be reckoned 

 in hundreds of thousands or millions of years, assures us that noth- 

 ing approaching a deep and powerful convulsion of our planet has 

 taken place within something like a million years. One naturally 

 concludes therefore that such supposed convulsions, which have 

 always been popular in geology, do not really take place at all. The 

 fact that the continents and islands show the preservation of suc- 

 cessive species of fossils, arranged in moderately conformable beds, 

 and the recognized proof that the great continents have never greatly 

 changed their places since geological history began, may be said to 

 supply decisive evidence that no deep-seated convulsions, such as 

 Elie de Beaumont and others were accustomed to imagine, ever take 

 place even at periods to be reckoned in millions of years. 



All important changes observed in the earth's crust must there- 

 fore be ascribed to external agencies, and especially to earthquakes, 

 which originate within forty miles of the surface, and seldom extend 

 to a depth greater than fifteen or twenty miles. Accordingly we 

 may dismiss for the present any further consideration of this prob- 

 lem; but we shall again resume it after we have examined the dis- 

 tribution of temperature and the secular movement of heat deep 

 down in our globe, which will give another proof that the interior 

 of the earth is now and always has been quiescent. 

 § 5. The Secular Propagation of Heat from the Nucleus into the 



Enclosing Shells zuould not Give Rise to the Contraction of mi 



Encrusted Planet. 



It was formerly held that the earth was a liquid mass stirred by 



