EARTHS. 



EARTHS. 



were found to yield the following proportion 

 of ashes 



1. Those fed by distilled water - 



2. Those fed by rain-water 



3. Those grown in the soil - 



Parts.' 



- 3-9 



- 7-5 



- 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, 

 by Bergman. Alumina, as far as 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 

 this earth 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 

 Davy, and is a natural process which cannot 

 but be interesting to the farmer. I merely 

 slightly alter his words in the following account 

 of this important natural phenomenon. It is 

 not difficult to comprehend the manner in which 

 this change is effected, and rocks converted 

 into soils, 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 

 lonu r 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 first the most rapidly. The feldspar 

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



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 

 tie atmosphere, and as these, too, decay, afford 

 more new materials to those already provided; 

 nd the decomposition of the rock still centi- 

 mes. At length, by such slow and almost 

 imperceptible processes, a soil is formed in 

 which even forest trees can fix their roots, and 

 vhich 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 

 >roduced by the decomposition of the granite 

 and sandstone rocks: such soils usually remain 

 or ages with only a thin covering of vegetation. 

 The soils produced by the same gradual means 

 on the limestones, chalks, and basalts, are often 

 clothed by nature with the perennial grasses, 

 and afford, when ploughed up, a rich bed of 

 vegetation 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 fertility. 

 This not only differs in different seasons, but 

 this power varies very considerably indeed in 

 oils, according to their chemical composition. 

 This was experimentally decided by Professor 

 Schubler, of the University of Tubingen, in his 

 Agronomy, or Principles of Agricultural Che- 

 mistry," 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. 

 (Journ. of Roy. Jig. Soc. 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 : 



