64 



PHYSICAL GEOLOGY 



movements are sudden, like those which produce earthquakes, 

 while others are very slow. 



The most effective movements are the slow ones, so 

 slow that in comparison the hour hand of a watch is revolving 

 rapidly. We cannot readily detect such changes while they 

 are in progress, but their results, after long periods of time, 

 are obvious. Slow movements of this .sort affect every- 

 thing from whole continents to the smallest invisible particles 

 of rock. Some of them may now be considered in more 

 detail. 



Warping of the surface. On the slopes of Mt. St. Elias, 

 in Alaska, modern sea shells have been found attached to the 



FIG. 45. Folded beds of limestone on the south coast of Alaska. (Stan ton 

 and Martin, U.S. Geol. Surv.) 



rocks just as they once grew, but several thousand feet above 

 the sea level. It appears that the coast has been slowly 

 raised above the sea to that extent. Conversely, on the 

 shores of North Carolina, stumps of trees are found stand- 

 ing out in salt water, where they did not grow. From this 

 it becomes evident that either the land has gradually sunk 

 beneath the sea, or the sea has risen upon it. There are 

 many other facts which prove that the surface of the earth 

 is rising in some places and sinking in others, but so slowly 

 that we do not perceive it. Slow upward and downward 



