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. Soil physics and management. leys but they also grind the materials into powder fitted forsoil formation. The work of moving water varies as the square ofthe velocitv- If the velocity is doubled the work that the stream iscapable of doing will be increased four times, since by doubling thevelocity, twice the number of particles will strike an object with.double the force. The deepening and widening of the stream chan- WEATHERING 17 nel is due mainly to the mechanical wear or friction of the materialcarried by the water (Fig. 9)- Clear water abrades very slowly.A rapidly flowing stream carrying large amounts of material abradesits bed very rapidly. This may be illustrated in the valleys thathave been cut by streams that contain water only after very heavyrains. Level plateaus have been dissected and changed into a ruggedcountry of hills and valleys by comparatively small wet weatherstreams. The entire land surface has been greatly modified by thisprocess and the transported material used largely in soil formation.. Fig. 10.—Inner gorge of Grand Canon of the Colorado River, Arizona. (Waleott, IT. S. Geol. Survey.) Captain C. E. Button ^ estimates that 10, 000 feet of rock stratahave been removed from an area of 13, 000 to 15^000 square milesby the Colorado Eiver (Fig. 10). When quartz is ground up through the action of moving watermuch sand is produced, and after these particles have been reducedto a certain size the permanent water film protects them largely fromfurther attrition. On the other hand, feldspars when suljjected toattrition form an impalpable mud or clay accompanied by consider-able loss of bases such as potassium, sodium, or calcium, accordingto the kind of feldspar.2 18 SOIL PHYSICS AND MANAGEMENT (e) Waves.—Wave action is confined to the shores of seas andthe larger lakes. In many places this agency breaks down solid cliffsinto masses of rock that become broken and worn into roundedboulders, then to pebbles, and finally into fine material that is