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In a moist climate where the quantity of rain that 

 falls annually equals from 40 to 60 inches, as in Lan- 

 cashire, Cornwall, and some parts of Ireland, a silice- 

 ous sandy soil is much more productive than in dry 

 districts; and in such situations, wheat arid beans will 

 require a less coherent and absorbent soil than in 

 drier situations; and plants having bulbous roots, will 

 flourish in a soil containing as much as 14 parts out 

 of 15 of sand. 



Even the exhausting powers of crops will be in- 

 fluenced by like circumstances. In cases where plants 

 cannot absorb sufficient moisture, they must take up 

 more manure. And in Ireland, Cornwall, and the 

 western Highlands of Scotland, corn will exhaust less 

 than in dry inlaitd situations. Oats, particularly in 

 dry climates, are impoverishing in a much higher de- 

 gree than in moist ones. 



Soils appear to have been originally produced in 

 consequence of the decomposition of rocks and strata, 

 It often happens that soils are found in an unaltered 

 state upon the rocks from which they were derived. 

 It is easy to form an idea of the manner in which 

 rocks are converted into soils, by referring to the in- 

 stance of soft granite, orprocelain granite. This sub- 

 stance consists of three ingredients, quartz, feldspar, 

 and mica. The quartz is almost pure siliceous earth, 

 in a crystalline form. The feldspar and mica are very 

 compounded substances; both contain silica, alumina, 

 and oxide of iron; in the feldspar there is usually 

 linre and pota*ssa; in the mica, lime and magnesia. 



