FREE BOOKS

Author's List




PREV.   NEXT  
|<   142   143   144   145   146   147   148   149   150   151   152   153   154   155   156   157   158   159   160   161   162   163   164   165   166  
167   168   169   170   171   172   173   174   175   176   177   178   179   180   181   182   183   184   185   186   187   188   189   190   191   >>   >|  
king extent, must be the figure of the earth. To the protuberant mass is due the precession of the equinoxes, which requires twenty-five thousand eight hundred and sixty-eight years for its completion, and also the nutation of the earth's axis, discovered by Bradley. We have already had occasion to remark that the earth's equatorial diameter exceeds the polar by about twenty-six miles. Two facts are revealed by the oblateness of the earth: 1. That she has formerly been in a yielding or plastic condition; 2. That she has been modeled by a mechanical and therefore a secondary cause. But this influence of mechanical causes is manifested not only in the exterior configuration of the globe of the earth as a spheroid of revolution, it also plainly appears on an examination of the arrangement of her substance. If we consider the aqueous rocks, their aggregate is many miles in thickness; yet they undeniably have been of slow deposit. The material of which they consist has been obtained by the disintegration of ancient lands; it has found its way into the water-courses, and by them been distributed anew. Effects of this kind, taking place before our eyes, require a very considerable lapse of time to produce a well-marked result--a water deposit may in this manner measure in thickness a few inches in a century--what, then, shall we say as to the time consumed in the formation of deposits of many thousand yards? The position of the coast-line of Egypt has been known for much more than two thousand years. In that time it has made, by reason of the detritus brought down by the Nile, a distinctly-marked encroachment on the Mediterranean. But all Lower Egypt has had a similar origin. The coast-line near the mouth of the Mississippi has been well known for three hundred years, and during that time has scarcely made a perceptible advance on the Gulf of Mexico; but there was a time when the delta of that river was at St. Louis, more than seven hundred miles from its present position. In Egypt and in America--in fact, in all countries--the rivers have been inch by inch prolonging the land into the sea; the slowness of their work and the vastness of its extent satisfy us that we must concede for the operation enormous periods of time. To the same conclusion we are brought if we consider the filling of lakes, the deposit of travertines, the denudation of hills, the cutting action of the sea on its shores, the undermining of cliff
PREV.   NEXT  
|<   142   143   144   145   146   147   148   149   150   151   152   153   154   155   156   157   158   159   160   161   162   163   164   165   166  
167   168   169   170   171   172   173   174   175   176   177   178   179   180   181   182   183   184   185   186   187   188   189   190   191   >>   >|  



Top keywords:
deposit
 

hundred

 

thousand

 

extent

 

mechanical

 
marked
 
brought
 

thickness

 
position
 

twenty


similar

 

distinctly

 
encroachment
 

manner

 
Mediterranean
 

measure

 
consumed
 
reason
 

inches

 

detritus


century

 

formation

 

deposits

 

concede

 

operation

 

enormous

 

periods

 

satisfy

 

vastness

 

prolonging


slowness

 
conclusion
 

action

 

cutting

 

shores

 
undermining
 

denudation

 
filling
 

travertines

 
rivers

countries
 

advance

 
perceptible
 
Mexico
 

scarcely

 

Mississippi

 
present
 

America

 
result
 

origin