ID GEOLOGY OF SOIL. 



not contain remains of animals or plants, it will be 

 found that the fossiliferous are neither granitic nor 

 trappean, yet are they to be classed with the last, 

 agreeing with them, in containing less silica, and 

 more lime, magnesia, and alumina. 



17. The stratified non-fossiliferous rocks agree in 

 chemical composition with the granitic, and the fos- 

 siliferous with the trappean and volcanic. 



18. The trappean and fossiliferous contain the 

 most lime and magnesia ; the granitic and non-fos- 

 siliferous, the most silex. The great difference in 

 chemical composition, between the two classes, is 

 produced by lime and magnesia, — two substances, 

 which, more than all others, have been thought to 

 influence the character of soil. 



19. The amount of this difference is about from 

 4 to 7 per cent.; yet notwithstanding this, the gene- 

 ral chemical constitution of all rocks approaches so 

 nearly to identity, that this may be laid down as the 

 first principle in agricultural chemistry, that there is 



ONE ROCK, CONSEQUENTLY ONE SOIL. 



20. To the farmer, all soil is primary. The 

 question then arises, how do rocks and soil affect 

 vegetation ? As a consequence of the first proposi- 

 tion, it may be laid down as the second principle of 



