Economical Geology of Massachusetts. 367 



of all successful cultivation. Its importance has been not so much overlooked as 

 undervalued. Hence, on this point the least light has been reflected from the 

 labors of Davy and Chaptal. It needs but a glance at any analysis of soils, pub- 

 lished in ihe books, to see that fertility depends not on the proportion of the earthy 

 ingredients. Among the few facts, best establislied in chemical agriculture, are 

 these ; that a soil, whose earthy part is composed wholly, or chiefly, of one earth ; 

 or any soil, with excess of salts, is always barren; and that plants grow equally 

 well in all soils, destitute of ^eme, up to the period of fructification, — failing of 

 geine, the fruit fails, the plants die. Earths, and salts, and gcine, constitute, then, 

 all that is essential ; and soils will be fertile, in proportion as the last is mixed with 

 the first. The earths are the plates, the salts the seasoning, the geine the food of 

 plants. The salts can be varied but very little in their proportions, without injury. 

 The earths admit of wide variety in their nature and proportions. I would resolve 

 all into ' jO-7-aniiic 5a?id ;' by which I mean the finely divided, almost impalpable 

 mixture of the detritus of granite, gneiss, mica slate, sienite, and argillite ; the 

 last, giving by analysis, a compound very similar to the former. When we look 

 at the analysis of vegetables, we find these inorganic principles constant constitu- 

 ents — silica, lime, magnesia, oxide of iron, potash, soda, and sulphuric and phos- 

 phoric acids. Hence these will be found constituents of all soils. The phosphates 

 have been overlooked from the known difficulty of detecting phosphoric acid. 

 Phosphate of lime is go easily soluble when combined with mucilage or gelatine, 

 that it is among the first principles of soils exhausted. Doubtless the good efi'ects, 

 the lasting efi^ects, of bone manure, depend more on the phosphate of lime, than on 

 its animal portion. Though the same plants growing in difl^erent soils are found to 

 yield variable quantities of the salts and earthy compounds ; yet I believe, that 

 accurate analysis will show, that similar parts of the same species, at the same age, 

 always contain the inorganic principles above named, when grown in soils arising 

 from the natural decomposition of granite rocks. These inorganic substances will 

 be found not only in constant quantity, but always in definite proportion to the 

 vegetable portion of each plant. The effect of cultivation may depend, therefore, 

 much more on the introduction of salts than has been generally supposed. The 

 salts introduce new breeds. So long as the salts and earths exist in the soil, so 

 long will they form voltaic batteries with the roots of growing plants ; by which, 

 the ' granitic sand' is decomposed, and the nascent earths, in this state readily solu- 

 ble, are taken up by the absorbents of the roots, always a living, never a mechan- 

 ical operation. Hence so long as the soil is granitic, using the term as above 

 defined, so long is it as good as on the day of its deposition ; salts and geine may 

 vary, and must be modified by cultivation. The universal diffusion of granitic di- 

 luvium will always affbrd enough of the earthy ingredients. The fertile character 

 of soils, I presume, will not be found dependent on any particular rock formation 

 on which it reposes. Modified they may be, to a certain extent, by peculiar form- 

 ations ; but all our granitic rocks afford, when decomposed, ail those inorganic 

 principles which plants demand. This is so true, that on this point the farmer al- 

 ready knows all that chemistry can teach him. Clay and sand, every one knows : 

 a soil too sandy, too clayey, may be modified by mixture, but the best possible 

 mixture does not give fertility. That depends on salts and geine. If these views 

 are correct, tlie few properties of geine which I have mentioned, will lead us at 

 once to a simple and accurate mode of analysing soils, — a mode, which determines 

 at once the value of a soil, from its quantity of soluble and insoluble vegetable 

 nutriment, — a mode, requiring no array of apparatus, nor delicate experimental 

 tact, — one, which the country gentleman may apply with very great accuracy ; and, 

 with a little modification, perfectly within the reach of any man who can drive a 

 team or hold a plough." 



