310 MISCELLANEOUS FARM SUBJECTS 



ing up the fine dust and carrying it for some distance. In this way 

 soils have been formed over large areas and others have been mod- 

 ified over still larger areas. 



Running water is also a very important agent in the formation 

 and distribution of soil material. During heavy showers more or 

 less water runs off the surface and coarse or fine particles are moved, 

 depending upon the volume and velocity of the moving water. 

 Even on comparatively level areas, some movement of soil material 

 takes place, but it is in the ravines, gullies, and streams that the 

 greatest amount of work is done by this agent. The volume and 

 velocity of the water in many streams is sufficient to move all sizes 

 of material, even to boulders weighing tons, and the crushing and 

 grinding that goes on during the movement of these boulders, 

 gravel, and sand is enormous. The finely ground up material as 

 well as that washed in by streams is carried by the larger creeks 

 and rivers and finally deposited, forming flood plains along their 

 courses, or deltas at their mouths. 



Glaciers have also been exceedingly important agents in the 

 formation and distribution of soil material. While they are usually 

 confined to arctic or mountainous regions, yet in times past, gla- 

 ciers in the form of moving ice sheets hundreds of feet thick came 

 down from the north, covering nearly all of the United States north 

 of the Ohio and east of the Missouri Rivers, extending as far south 

 as the Ozark Ridge. As this ice sheet advanced from the north, 

 picked up, pushed and carried along with it rocks of all sizes, shapes 

 and kinds. 



The grains of sand, silt, and clay contained in all soils con- 

 sist of a large number of minerals, such as are also common to and 

 make up the bulk of all common rocks, and, in addition, of very 

 insoluble decomposition or alteration products. If a small sample 

 of soil is thoroughly washed by decantation, being repeatedly pes- 

 tled or violently shaken in a bottle with the water so as to loosen all 

 the grains and wash out the fine material, or if it is merely acted 

 upon by a dilute acid to remove the highly colored iron compounds, 

 the variety of color and of form to be seen with the naked eye or 

 with a hand lens will indicate the variety of mineral constituents. 

 The common rock-forming and soil-forming minerals are 



Quartz. Pyroxenes. 



Limonite Turgite series. Chlorites. 



Hematite. Tourmaline. 



Kaolin or kaolin ite. Rutile. 



Feldspars. C^lcite. 



Micas. Dolomite. 



Apatite. Selonite. 



Hornblendes. Zeolites. 



These minerals contain potash, phosphoric acid, lime, mag- 

 nesia, and other mineral plant food. 



Rain, wind, frost, glacial ice, streams, waves, plants and ani- 

 mals, and the solvent power of water, are at work continually on 

 every exposed rock. By these agencies mountains have been re- 



