THE HISTORY OF THE GROUND. 2C) 



the history of the earth wonderful changes that have 

 also had a great influence in giving the surface of the 

 earth its present appearance. Earthquakes have raised 

 mountains in the air. Volcanoes have lifted enormous 

 heaps of lava, dust, and ashes into the clouds, or scat- 

 tered vast quantities of cinders over whole tracts of 

 country. The sea has rolled in upon the land. The 

 lands have even sunk in the water, or been raised up ; 

 and this many times over, so that what were once 

 shallow bays and lagoons became at last mountain- 

 tops. Vast tracts of gravel scattered by streams from 

 old dead mountains have been hardened into stone. 

 Deep black pools of mud have been sunk and crushed 

 in earthquakes, and turned to coal. Whole beaches 

 have been solidified to red sandstones by water charged 

 with iron filtering through the sand. 



Moreover, climates have changed. Where now we 

 have each season snow and ice in winter, and growing 

 plants and hot sunshine in summer, there was at one 

 time almost continual winter. It is now thought, that 

 for a very long time all of New England, New York, 

 and several other States, were buried out of sight under 

 deep ice. This ice, like the glaciers we see to-day in 

 high mountains, drifted slowly southward over the 

 country, ploughing up the loose earth, grinding the 

 hard faces of the rocks till they were polished like 

 mirrors, cutting deep grooves in the rocks, and push- 

 ing enormous quantities of mud, stones, and gravel 

 through all the valleys. Schunemunk Mountain bears 

 upon its smooth rounded top hundreds of traces where 



