. Elementary physical geography . round water; andarmed with these, it possesses great solvent power. Whenthe water has percolated to a considerable depth in the earth,its temperature is so raised that its power is greatly some cases it obtains a temperature higher than the boil-ing point at the surface ; and then it becomes a powerfulsolvent, partic-ularly if it isarmed withacids or it reachesthe surface inthe form of aspring, we veryoften find proofthat under-ground water isengaged in thiswork of solu-tion. Many ofthese are min-eral springs, andat times, depositsof
. Elementary physical geography . round water; andarmed with these, it possesses great solvent power. Whenthe water has percolated to a considerable depth in the earth,its temperature is so raised that its power is greatly some cases it obtains a temperature higher than the boil-ing point at the surface ; and then it becomes a powerfulsolvent, partic-ularly if it isarmed withacids or it reachesthe surface inthe form of aspring, we veryoften find proofthat under-ground water isengaged in thiswork of solu-tion. Many ofthese are min-eral springs, andat times, depositsof iron, or othersubstances, aremade where the water reaches the surface. When hot waterescapes at the surface, as is the case in the geyser regionof the Yellowstone Park, extensive chemical deposits of rockare sometimes formed around the springs (Fig. 105). Thereason for the deposit of these substances, is sometimes thatthe temperature of the water is lowered, and its solventpower thereby decreased; in other cases it is due to the. Fig. 105. Deposits of carbonate of lime, Pulpit terrace, Mammoth Hot Springs of Yellowstone Park. 226 PHYSICAL GEOGRAPHY. escape of certain gases which gave to it much of its power;and it is often the result of chemical changes in the presenceof the air. Even in the earth, for one reason or another, thewater at times deposits some of its dissolved load. This isone of the ways in which rocks are cemented ; and it appearsto be one of the causes for the formation of some of thevaluable mineral deposits. Underground water is also engaged in the work of chang-ing some of the minerals of the rocks. It actually causesa decay of some minerals, and brings about very importantchanges in others. This is one of the ways in which therocks are broken into fragments, and soils formed. This
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