JOHN P. NORTON'S ADDRESS. 



229 



A mixture of the two first minerals in this table, felspar and 

 mica, with common quartz or silica, forms granite. In some 

 granites, however, the place of mica is almost or entirely sup- 

 plied by the third mineral, hornblend. Now it will be observed 

 that in the two first columns no lime is mentioned, but in the 

 third there is rather more than twelve per cent. ; here will re- 

 sult a notable difference in the soils formed from granites con- 

 taining hornblend, and those which contain only felspar and 

 mica. 



In the fourth column is named hypersthene, a rock resem- 

 bling in appearance some of the hornblend rocks ; but contain- 

 ing little lime, no potash or soda, much magnesia, and a third 

 of its weight of protoxide of iron, a substance most injurious 

 to vegetation when in large quantity. 



Serpentine, a rock which forms many soils, has nearly half 

 its weight of magnesia. Between basalt and greenstone, allied 

 species of rocks, are also seen very marked differences. 



These instances show that much light as to composition of 

 any soil, may be gained by a knowledge of the particular rock 

 from which it was wholly or chiefly formed. Reasoning as 

 above, we may ordinarily derive some general rule which shall 

 hold good over a particular district. 



If not absolutely certain in all cases, we may at least in this 

 way work out a judicious series of experiments, for the purpose 

 of ascertaining, with as little expense as possible, what is the 

 most advantageous and economical application to any given 

 soil. 



Beyond this, the great mass of farmers cannnot go, for the 



