EFFECTS OF THE MOVEMENTS OF WATER 29 



there are many places where the edges of continents have 

 sunk below the sea. This is true near New York City. 

 The valley of the Hudson River is what is called a " drowned 

 valley"; a long time ago it sank below the sea-level, so 

 that now sea-water mingles with the river-water for many 

 miles above the mouth. Careful measurements have 



FlG. 6. Photograph showing how running water cuts away the softer parts of 

 the land and leaves the harder rocks sticking up. 



proved that the coast of Massachusetts is sinking very 

 slowly. You have seen how air and water keep moving, 

 and now you learn that the solid part of the earth also 

 keeps moving. Change follows change. All nature is just 

 an endless procession of changes. Not even the hardest 

 rock is quite the same this year that it was last year. 



So we see that, while running water keeps wearing the land 

 down, hidden forces inside the earth keep lifting it. The re- 

 sult is that there is just about the same amount of dry 



