THE CONQUEST OF NATURE 



growth of certain forms of vegetation, or to the arrange- 

 ment of such growth. Alterations in the color of the 

 rocks on a hillside are also important guides, as such 

 discolorations frequently indicate that oxidizable min- 

 erals are located above. 



In hilly or mountainous regions, where the under- 

 lying rocks are covered with earth, portions of these 

 surfaces are sometimes uncovered by the method 

 known as " booming." In using this method the 

 prospector selects a convenient depression near the 

 top of a hill and builds a temporary dam across 

 the point corresponding to the lowest outlet. When 

 snow and rain have turned the basin so formed into 

 a lake, the dam is burst and the water rushing down 

 the hillside cuts away the overlying dirt, exposing 

 the rocks beneath. This method is effective and in- 

 expensive. 



The beds of streams, particularly those in hilly and 

 mountainous regions, are fertile fields for prospecting, 

 particularly for precious metals. Stones and pebbles 

 found in the bed are likely to reveal the ore-founda- 

 tions along the course of the stream, and the shape 

 of these pebbles helps in determining the approximate 

 location of such foundations. An ore-bearing pebble, 

 well worn and rounded, has probably traveled some 

 little distance from its original source, being rounded 

 and worn in its passage down the stream. On the 

 other hand, if it is still angular it has come a much 

 shorter distance, and the prospector will be guided 

 accordingly in his search for the ore- vein. 



But prospecting is not limited to these simple sur- 

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