300 Our Surroundings 



wearing away of solid rock. The particles carried away by the 

 water have been deposited elsewhere as part of the soil. The gorge 

 at Niagara Falls was formed by the gradual erosion of rock. 

 Water gets into crevices in rocks and freezes, breaking off small 

 particles. This is an important factor in making soil. 



Glaciers. In all parts of northern United States and in other 

 countries there 'are found evidences of ancient glaciers, or ice 

 sheets. Ages ago these great masses of ice and snow covered a 

 vast section of the northern hemisphere. They moved like im- 

 mense rivers, except that the motion was so slow that it was not 

 noticeable. As they moved they carried along rocks, loose soil, 





Blown Brothers. 



AN ALASKAN GLACIER 

 A river of flowing ice. 



small stones, and boulders of various sizes, and when they melted 

 in warmer climates they deposited these along their courses. Such 

 glacial deposits may be seen in various sections of the country. 

 As the ice sheets moved over the rocks they rubbed off small 

 particles that today form a part of the soil of the earth. Glacial 

 soils are usually fertile. 



Wind. Wind aids in the formation of soil by striking against 

 walls of rock and causing small parts to break off which gradually 

 disintegrate and become soil. Sometimes the wind picks up gritty 

 stone particles and drives them against the rock masses, wearing 



