EARTHS. 



were found to yield the following proportion 

 of ashes 



Part*. 



1. Those fed by distilled water ... 3 

 3. Those fed by rain-water - - - 7-5 

 3. Those grown in the soil - 12 



The mode in which the earths are absorbed 

 by the roots of the plant is, it is almost certain, 

 by means of their solution in water, for both 

 carbonate of lime and silica are, in small pro- 

 portions, soluble in water ; they exist together 

 in many springs ; and they were both found in 

 the water of the Clyde by Dr. Thomson, in that 

 of the Thames by Dr. Bostock, and in the 

 springs of Upsula, celebrated for their purity, 



:man. Alumina, as far a* we know, is 

 not soluble in water, but then it exists in very 

 small proportions in plants; and the soluble 

 salts of which it is the base may serve to yield 



rth to vegetables : the earth itself is so- 

 luble in ammonia. 



The way in which soils are gradually formed 

 by the action of the atmosphere upon the hard 

 primitive rocks has been well explained by 

 ; :nd is a natural process which cannot 



but be interesting to the farmer. I merely 

 slightly alter his words in the foil. >wing account 

 of thi^ important natural phenomenon. It is 

 not difficult to comprehend the manner in which 

 this chan-e is effected, and rock> converted 

 Is, by referring to the instance of soft 

 granite or porcelain granite. This substance 

 is composed of three ingredients, quartz, feld- 

 spar, and mica. The quartz is almost pure 

 silicious earth in a crystalline form. The 

 feldspar and mica are very compound sub- 

 stances ;* both contain silica, alumina, and 

 oxide of iron: in the feldspar there is usually 

 lime and potash ; in the mica, lime and mag- 

 nesia. 



When a granitic rock of this kind has been 

 long exposed to the action of the atmosphere 

 the lime and the potash contained in its consti 

 tuent parts are acted upon by water or carbonic 

 acid; and the iron, which is almost always in 

 its least oxidized state, tends to combine with 

 more oxygen ; the consequence is, that the 

 feldspar decomposes, and likewise the mica 

 but the fijst the most rapidly. The feldspar 

 which is, as it were, the cement of the stone 

 forms a fine clay; the mica, partially decom 

 posed, mixes with it as sand, and the undecom 

 posed quartz appears as gravel, or sand o 

 different degrees of fineness. As soon as thi 

 smallest layer of earth is thus formed on th 



* Common felspar is composed of- 

 Silica .... 

 Alumina .... 

 Lime - - - - - 

 Oxide of iron ... 

 Potash .... 

 Loss 



Common mica is composed of 

 Silica ... 

 Alumina ... 

 Oxide of iron - 

 Oxide of manganese 

 Potash ... 



62S3 

 1702 

 300 

 1-00 

 1300 

 3-50 



100- 



47-00 

 20-00 

 1550 



175 

 1450 



1-25 



100 



EARTHS. 



urface of a rock, the seeds of lichens, mosses, 



nd other imperfect vegetables, which are con- 



tantly floating in the atmosphere, and which 



ave made it their resting-place, begin to vege- 



ate; their death, decomposition, and decay 



fford a certain quantity of organic matter, 



hich mixes with the earthy materials of the 



ock. In this improved soil, more perfect 



lants are capable of subsisting; these in their 



urn absorb nourishment from water and from 



atmosphere, and as these, too, decay, allot d 



more new materials to those already provided 



nd the decomposition of the rock still eonti 



ues. At length, by such slow and* almost 



mperceptible processes, a soil is formed in 



vhich even forest trees can fix their roots, and 



which is fitted to reward the labours of the cul- 



ivator. 



Where successive generations of vegetables 

 lave grown upon a soil, unless they have been 

 carried off by man or consumed by animals, 

 he vegetable matter increases to such an ex- 

 ent that the soil approaches to peat in its 

 nature. Poor and hungry soils are commonly 

 M-odiiced by the decomposition of the granite 

 ind sandstone rocks: such soils usually remain 

 or ages with only a thin covering of vegetation. 

 The soils produced by the same gradual means 

 m the limestones, chalks, and basalts, are often 

 clothed by nature with the perennial grasses 

 and afford, when ploughed up, a rich bed of 

 n for every species of cultivated crop 



The quantity of moisture which a soil, or the 

 earths of which it is chiefly composed, contain, 

 nfluences to a very material extent its t. rtility 

 This not only differs in different seasons, but 

 this power varies very considerably indeed in 

 soils, according to their chemical composition. 

 This wa> experimentally derided by Professor 

 Schubler, of the University of Tubingen, in his 

 " Agronomy, or Principles of Agricultural Che 

 ." for a translation of which the English 

 farmer is indebted to Mr. Hudson, the present 

 excellent Secretary to the Royal Agricultural 

 Society of England, a translation of which 

 I have largely availed myself in this paper. 

 (Joitrn. of Roy. Jig. Sor. vol. i. p. 177.) M. Schu- 

 bler found that a cubic foot of different soils, 

 when thoroughly saturated with water and 

 when completely dried, weighed as follows : 



The result of these trials will be useful to 

 the farmer in explaining to him the reason 

 why, on account of their requiring more or less 

 moisture, certain crops flourish best on parti- 

 cular soils ; and even in the carriage of the 

 earths he will perceive that their weight in th 

 wet or dry state is much greater than some 

 persons suppose. 



