THE FORMATION OF THE SOIL. 121 



these spreading out under the great depths were soon pressed 

 and hardened into the slates or the sandstones which we 

 know so well. The hot water holding silica in Solution gave 

 up its burden as it cooled, and gradually added it to these 

 beds furnishing the cement which bound them into a firm 

 mass; or it filled the fissures and formed the quartz beds and 

 veins so prominent among the existing mountain masses. 



Then came long periods of rest. The ocean cooled and ' 

 no longer gave forth the vast clouds of steam which hid the 

 sun. Then came the light, and the day and night. The 

 dry land was formed by the lifting up of the earth's crust 

 along continuous lines ; the rocks being broken and tilted 

 on their edges, and higher in places than in others, formed 

 lines of islands through the enveloping ocean. Thus were 

 formed the great chain of the Rocky mountains, and the 

 lesser chain of the Blue ridge and Appalachians which stretch 

 from Georgia to the north into lower Canada, and of which 

 the White mountains and the Adirondacks are a part. A 

 great broad valley was formed between these mountain 

 chains, and a gradual slope on either side down to the 

 depths of the ocean. By gradual shrinking of the still cool- 

 ing crust, the mountain chains were lifted up and great de- 

 pressions were formed into which the ocean withdrew, leav- 

 ing broad continents stretching from the south to the north 

 poles. All these changes of course were accompanied by 

 vast floods which washed the loose materials into depres- 

 sions and formed layers of gravel, sand, clay and earth, much 

 as we find them to-day w r hen w r e excavate the banks of earth 

 on the hill sides. 



Then came the ice period. Everywhere over half the 

 earth's surface were vast beds of ice. These spread from 

 the mountain tops down their sloping sides to the valleys. 

 As the lower portions melted, the pressure of the enormous 

 masses above, forced these beds of ice downwards, slowly 

 but continuously ; as the glaciers of the present age move 

 down the mountain sides. The tremendous pressure ground 

 down the rocks into powder; w r earing away thousands of 

 feet from the top, cutting off the crests of huge bends and 



