SOIL FORMATION 75 



"As soon as a stream is fairly over the lake lip it breaks into 

 a cascade, never for a moment halting, and scarce abating one 

 jot of its glad energy until it reaches the next basin. Then 

 swirling and curving drowsily through meadow and grove it 

 breaks forth anew into gray rapids and falls, leaping and gliding 

 in glorious exuberance of wild bound and dance down into an- 

 other and yet another lake basin." Many of the best agricultural 

 soils were formed in just this way, and they owe their great 

 depth and great fertility to their method of formation. 



Action of Waves. — ^The wind lashes the water of lakes and 

 oceans against their shores and in so doing rolls rocks up and 

 down their beaches. This action, together with the various sus- 

 pended substances in the surf, slowly wears away the rock. 

 Throughout the Great Basin the history of the extinct lakes may 

 be read from the wearing eilect of their waters upon the sur- 

 rounding mountains. 



Ice.— In the early geologi cal periods great sheets of ice cov- 

 ered many paTi^^fl&W^ flowed slowly as does 



water from the highlands into the lowlands. On their journey 

 they froze around monstrous bowlders which they dragged slowly 

 along, grinding one another and the underlying rock into a fine 

 powder. Rocks from the overhanging cliffs were caught up by 

 the surface of the glacier and transported to lower levels. 



Volcanoes—During the eruption of volcanoes large quanti- 

 ties of lava, gases, and fragments are ejected. The lava is a 

 solution of various minerals made fluid by heat. This often flows 

 from vents as would water. Some lavas flow only a short dis- 

 tance before becoming chilled and stiff. However, the basic 

 lavas which yield the best soil often flow long distances and 

 cover large areas. In earlier geological times such floods of lava 

 overspread areas in Idaho, Washington, and Oregon, estimated at 

 over 200,000 miles in extent and with an observed thickness in 

 places of hundreds of feet. These easily weather, yielding deep 

 productive soil which under favorable moisture conditions is 

 very fertile. 



The solid matter thrown from volcanoes consists of large 



