LAND AND WATER. 29 



raised them more and more above the level of the water. 

 The first appearance of the North American continent 

 was in a small, angular section, extending from the Great 

 Lakes northeast to Labrador, and northwest to the 

 Arctic Ocean. 



North America in the Tertiary Era. (White indicates land.) 



Mountains and Hills. The cooling and shrinking of the 

 continent has also given rise to mountain ranges and 

 valleys. The imvnnl pressure and sinking of certain 

 sections caused long cracks in the earth's crust, and the 

 upturned edges have formed some of the great mountain 

 ranges of the earth. 



Some mountains have also been formed by an accumu- 

 lation of melted matter poured from these cracks and 

 from volcanoes, 



