262 



ANALYSES OF SOILS. 



The variation in composition would appear still farther liy other analyses : thus, the 

 silex in .some of the Vermont concretion.s amounts to 29'OS ; the alumina varies from 7 -30 

 to 2S"40 per cent ; the peroxide of iron, from 1'73 (o S'81 per cent. 



Sulphate of lime, wliicii is a common substance in the Albany clay, is not found in the 

 concretions. The largest and most spherical ones seem to be formed where carbonate 

 of lime is in the greatest abundance. In many instances, the same material which forms 

 the claystone, forms, in the clay bed.s, distinct layers, in some of whicli silex instead of 

 carbonate of lime is the predominant ingredient. The force which produces a concretion 

 is closely allied to that of crystallization, for there is a tendency to build up regular sym- 

 metrical solids. It is active in all semiconsolidated materials, as paste, mortars and clays ; 

 and it always begins at a centre, and extends in the direction of the radii of a sphere. 



Paring and burning of clay soils. 



In this place the question comes up, what changes should clays be made to undergo, in 

 order to become fitted for cultivation 1 Some maintain that the iron contained in clay is 

 converted by combustion into a peroxide ; the former state of the iron being noxious, and 

 the latter congenial to vegetation, or else becoming so by its relations to other elements 

 existing in the soil. Others suppose that it is the sulphuret of iron, existing in clay soil, 

 which is converted into the peroxide by burning ; and that the sulphuret of iron is injurious 

 to vegetation. This o])inion can not be correct, unless indeed the sulphuret is of tliat kind 

 which decomposes and forms sulpliale of iron, which, in largo doses, is uniiueslionably 

 injiirious to plant.s. We can hardly believe that sulphuret of iron is at all injurious, unless 

 it is undergoing decomposition. Admitting the correctness in part of this view, still the 

 mechanical effect of the burning is far more important than the chemical effect. Clay, 

 as deposited, is close, impervious, or difficult to be penetrated by the roots of plants. Two 

 effects follow from binning : 1st. The soil is rendered open, pervious, and penetrable ; 2. 

 Some of llie matters in the clay become more soluble. This is maintained by Liebig, who 

 supports his view of the subject by reference to tlie greater soluliility of argillaceous earths 

 in acids after they are ignited, than before. It is true, we believe, however, that the peroxide 

 of iron does exert a salutary influence on vegetation ; and this opinion is supported by the 

 character of the productions of a brick red soil. This is certainly found to be a warm soil, 

 there being a perceptible difference in favor of the growth of grass and grain on lands of 

 this color ; and it would seem that sheep and cattle are fond of grazing upon these soils, 

 and give them a preference. It appears, then, 1st, that the burning of clays of any kind 



