CHEMISTRY. 227 



saturated with carbonates the siUca is precipitated. If so/ it is not difficult 

 to understand how a continuous precipitation of silica may have taken 

 place while the carbonates were cari-ied off in solution. 



It has been explained that the District shows very small evidences of 

 erosion since the deposition of ore began — less than one would suppose com- 

 patible with the deposition of quartz from flowing springs on so large a 

 scale. The District presents many points of similarity to the neighbor- 

 hood of Steamboat Springs, where but little water flows off", while abundant 

 columns of steam constantly rise from many vents. If, as seems probable, 

 the condition of things at Washoe was similar, the precipitation of silica 

 must have been greatly accelerated by concentration of the solutions through 

 evaporation. Precipitated silica is, of course, in great part amorphous, but 

 its conversion into quartz is a well-known change. 



'This statement is do doubt founded on experiments, of which I have failed to find an accoont. 



