4 AGRICULTURE FOR BEGINNERS 



soil to cover a square mile of surface to a depth of two 

 hundred and sixty-eight feet. 



The early brooks and rivers, instead of bearing mud, 

 ran oceanward bearing ground stone that either they them- 

 selves had worn from the rocks by ceaseless fretting, or 

 bearing stones that other forces had dislodged from parent 

 nest. The large pieces were whirled from side to side, 

 beaten against one another, or against bed rock, until they 

 were ground finer. The rivers distributed this rock soil just 

 as the later rivers distribute muddy soil. Year after year 

 for ages the moving waters ground against the rocks. Vast 

 were the waters ; vast the number of years ; vast the results. 



Glaciers were another soil-producing agent. Glaciers, 

 as Stockbridge says, are but " streams frozen and moving 

 slowly but irresistibly onwards, down well-defined valleys, 

 grinding and pulverizing the rock masses detached by the 

 force and weight of their onslaught." Where and how 

 were these glaciers formed ? 



Once a great part of upper North America was a vast 

 sheet of ice. Whatever moisture fell from the sky fell 

 as snow. No one knows what made this long winter of 

 snow, but we do know that snows piled on snows until 

 mountainlike masses reared their heads above the rocks. 

 The lower snow was by the pressure of the upper packed 

 into ice masses. By and by some change of climate caused 

 these masses of ice to break up somewhat and to move to 

 the south and west. These moving masses, carrying rock 

 and frozen earth, ground them to powder. King thus 

 describes the stately movement of these snow mountains : 

 " Beneath the bottom of this slowly moving sheet of pressure- 

 plastic ice, which with more or less difficulty kept itself 



