MANURES. 51 



careous soils, that the straw is always firm and upright, 

 whatever may be the weight of the bending ear at the top. 

 By a deficiency of silicates, we mean, that they do not exist 

 in a soluble form, which is the only state in which plants 

 can seize upon and appropriate them. The efforts of some 

 roots in procuring this indispensable food, have been so irre- 

 sistible, as to have decomposed the glass vessels in which 

 they have been grown. Before using it as a manure, the 

 glass should be reduced to powder by grinding. 



CRUSHED MICA, FELDSPAR, LAVA, THE TRAP ROOKS, &c. 



Feldspar contains 66.75 of silica; 17.50, alumina; 12, 

 potash; 1.25, lime ; and 0.75, oxide of iron. Mica consists 

 of silica, 46.22; alumina, 34.52; peroxide of iron, 6.04; 

 potash, 8.22; magnesia and manganese, 2.11. Most of the 

 lavas and trap-rocks hold large quantities of potash, lime, 

 and other fertilizing ingredients. The last frequently form 

 the entire soils in volcanic countries, as in Sicily, and around 

 Mount Vesuvius in Italy, in the Azores and Sandwich 

 Islands ; and their value for grains and all cultivated plants, 

 is seen in the luxuriance of their crops and the durability of 

 their soils. These examples illustrate the great influence 

 of saline manures, and their near approach to an entire in- 

 dependence in sustaining vegetation. Whenever they be- 

 come exhausted by the savere usage they undergo, two or 

 three years of rest enables them again to yield a remune- 

 rating crop to the improvident husbandman. 



Granite, sienite, and some other rocks, yielding large 

 proportions of potash and some lime, abound throughout 

 the eastern portion of this country. The potash in them, is 

 however, firmly held in an insoluble state ; but if they are 

 subjected to a strong heat, they may then be easily crushed, 

 when they yield the potash freely by solution. In this con- 

 dition, they constitute a valuable top-dressing for almost 

 every soil and crop. 



It is a subject of frequent remark, that the soil underneath, 

 or in immediate contact with certain walls, which have 

 been erected for a long period, is much richer than the ad- 

 joining parts of the same fields. This difference is probably 

 due, in some measure, to the slow decomposition of import- 

 ant fertilizers in the stone, which are washed down by the 

 rains, and become incorporated in the soil. The removal of 

 stones from a fertile, .field, has been deprecated by many an 

 observing farmer, as materially impairing its productiveness. 



