General Discussion 



225 



Comparing these two statements, and illustrating them by 

 means of the following diagram (fig. 16), it is evident that the 

 depreciation in yield observed in the upper plots in 1905 has dis. 

 appeared in 1916, the yields on the last date being practically 

 uniform from top to bottom of the field. Effects of tailings are 

 still plainly visible in plots 1 and 2 in spots and patches of short 

 alfalfa, compensated for, however, by areas of stimulated growth 

 apparently due to seepage from the adjacent ditch. The yield 

 of the field as a whole is also much improved due to cultivation 

 and reseeding of the field. 



In brief it may now be stated that, following the exclusion 

 of tailings from the irrigating waters of this locality, it has been 

 found possible, in this carefully observed case, to overcome the 

 deleterious effects of tailings deposits upon alfalfa, slowly but 

 almost entirely, in about ten years. 



Thus, co-operation between miners, in restraining tailings 

 from irrigating streams, and those farmers who cultivate their 

 alfalfa intelligently, effectually disposes of the most serious prob- 

 lem that has arisen in connection with copper-mining detritus. 

 ■ The chemical composition of tailings, in fact, would indicate 

 that, as in the case of humid region subsoils, when they are en- 

 riched by the addition of organic matter and nitrogen, and filled 

 with bacterial life, they may make very good soil. Following 

 is a statement of the composition of four representative samples 

 of ores and tailings, with reference to potash and phosphoric 

 acid : 



