PRECIPITATION OF THE METALS. 1083 



from different sources meet. Such precipitation takes place under the 

 general law that when solutions of two or more kinds are mingled, if a 

 substance can form which is insoluble in the liquids present, this compound 

 will be produced and precipitation take place. This mingling of solutions 

 is probably the most important of the causes of precipitation of ores. 



It is evident that solutions from different sources enter a given trunk 

 channel at many places and thus a multitude of streams with different 

 composition mingle in a trunk channel. Each of the incoming streams is 

 different from any of the others, although in many cases the difference may 

 be slight. As a case of certain considerable difference may be mentioned 

 ascending and descending streams. (See pp. 1175-1177.) If in a chemical 

 laboratory a multitude of solutions be taken at random and thrown together 

 precipitates will be almost certain to form, and in an underground channel 

 the same effect is likely to be produced when the various solutions come 

 together. This mingling of solutions is one of the most important of all 

 the factors which results in the deposition of the ores. I have little question 

 that the wide variety of solutions which enter a given channel explain in a 

 large measure the exceedingly irregular richness of ore deposits. Where 

 a metal is found abundantly in a fissure the explanation in many cases is 

 certainly that at or near that place there entered a stream which carried 

 either the precipitated metal or an agent capable of precipitating it from a 

 solution already in the trunk channel. For instance, it is believed that at or 

 near the place where the great bonanza of the Comstock lode was found, 

 there entered either solutions rich in gold and silver, or a solution having a 

 compound which precipitated the gold and silver already traveling* upward 

 within the lode. Perhaps the former hypothesis is the more probable. 



Ore shoots, or chimneys of ore of exceptional richness, occur very 

 frequently in veins. They are sometimes parallel with the dip and at 

 other times pitch to the right or left of it. The locations of these ore shoots 

 in many instances I believe were controlled by cross fractures or joints 

 through which entered waters, carrying either metalliferous material or 

 solutions capable of precipitating the metalliferous mineral in the trunk 

 channel at the place where the lateral streams of water entered. 



The lead and zinc deposits of the Mississippi Valley, according to 

 Jenney, are larger at the crossings of two sets of fissmes than elsewhere. 

 This may be explained partly by the greater abundance of the solutions 



