GEOLOGY OF SOIL. 31 



ited portion of our country ; that the analyses have been 

 conducted l>y a new process ; that the soil examined rests 

 chiefly on granitic rocks, and has been thence derived. Had 

 the field been wider, or the process different, the results 

 would have been different. 



All analysts, from the earliest times, have found a very 

 large per centage of soil insoluble in acid or alkali. The 

 object of chemists has been, by the aid of water and weak 

 acids, by the gentlest means to separate the elements 

 of soil. Others have used fiercer means, and have attacked 

 the insoluble portion of soil, by means common to the 

 analysis of intractable stones, by fusion with alkali, followed 

 by treatment with acid. By either mode the mineral part 

 of soil is separated into two general divisions, into soluble 

 and insoluble portions. 



This is to be observed of all soil analyses, by whomsoever 

 or howsoever made, that while all are imperfect approxima- 

 tions only, to truth, yet the insoluble ingredients are the 

 substances which from their chemical constitution are least 

 affected by the various modifications to which soil analyses 

 have been subjected. Whatever modes may have been 

 used, in all, the insoluble substances make up the great bulk 

 of soil presented in the per centage result, as, "silica, 

 silicious residuum, sand and clay, insoluble mineral matter, 

 fine earthy matter, sandy residuum." 



In the analytical results, alumina, or clay, oxide of iron, 

 or iron rust, and magnesia, are frequently stated in separate 

 amounts. These substances have been educed by analysis 

 from their combinations, yet are they for the most part a 

 portion of the insoluble compounds variously designated 

 above, and should be included in that class. The " alumin- 

 ous residuum," or clay, is certainly an earthy compound 

 only. 



