Observations on Liehig^s " Organic Chemistry'^ 125 



alkalies in soils, we will be apt to be misled. In the latest work on 

 mineralogy, by Mr. Allan, analyses are given, by many chemists, 

 of different varieties of feldspar, in many of which the potash is 

 absent, and its place supplied by lime and magnesia ; in the 

 prismatic common sort it is stated as high as 13 per cent. In 

 mica, many varieties under different names are stated as con- 

 taining no potash, but variable quantities of the other alkalies: 

 in mica, properly so called, and in talc mica, six different analyses 

 give the potash as varying from 5 to nearly 15 per cent, and 

 the magnesia from 9 to 26 per cent. Dr. Liebig's estimate 

 differs from this. The proportion of the different minerals in 

 the different rocks is more various still. Feldspar is generally 

 allowed to be the greatest source of potash, and is found in 

 greatest quantity in the igneous or volcanic rocks, as granite, 

 greenstone, basalt, and other trap rocks. Granite in Bavaria is 

 stated by Dr. Liebig as forming a fertile soil ; but in Scotland 

 and England the soils lying on granite are proverbially barren, 

 from their high, bleak, and cold situation, and the thinness of the 

 stratum of soil. Clay soil, the professor says, generally contains 

 most alkali; hard stones of the order gem contain fewer alkalies 

 than those of the order spar, which are softer and more clayey ; 

 but some minerals containing a great deal of alumina are almost 

 destitute of potash. 



The action of rivers and currents has great effect on soil, 

 according as they carry off" or silt over the ground. In the soils 

 in this neighbourhood, which are formed from the debris of 

 sandstone lying above the carboniferous series, and of green- 

 stone or whin disrupted up through it, we have all varieties of 

 soils, from light sandy to stiff" clayey. The one side of the 

 river is all inclining to sandy; the other is generally clayey. 

 In wet seasons the best crops are had on the sandy soils, which 

 are generally warmer and drier, and about a month earlier in 

 springing ; in warm dry seasons the clayey soils, if pulverised, 

 yield the best crops. Some manures, as cow-dung, retain more 

 water than others; and there is much of the art of cultivation lies 

 in preserving both heat and moisture, which are essential as well 

 as alkalies. The composition of a soil and its proper pulveri- 

 sation facilitate the entrance of heat and moisture, and retain 

 them to assist with the air in the decomposition of the food ; and 

 different soils and seasons require different management. On 

 this subject I treated more largely than I have room for here, 

 in my former esssay on Dr. Lindley's work. In our deep al- 

 luvial soils, when the alkalies are exhausted by one crop, the 

 disintegration of the rock many feet buried below the surface 

 will go on very slowly : it should take many crops, I think, to 

 exhaust a soil of alkalies. Many crops of wheat are successively, 

 in rotation, taken from ground which gets nothing but ordinary 



