ARBORICULTURE. 327 



proceeding probably from decomposition of the water ; but, 

 partly, it may be presumed, from its capacity of abstracting a 

 portion of air from tbe atmospbere, which the soil at least is 

 capable of doing. The following is the analysis of a fertile soil, 

 as occurring in the neighborhood of Bristol, England. In 400 

 grains, there were of water, 5*2; siliceous sand, 240; vegetable 

 fibre, 5 ; vegetable extract, 3 ; alumine, 48 ; magnesia, 2 ; oxide 

 of iron, 14 ; calcareous earth, 30 ; loss, 6. But Kirwan has 

 shown in his Geological Essays, that the fertility of a soil depends 

 in a great measure upon its capacity for retaining water ; and if 

 so, soils containing the same ingredients must be also equally 

 fertile, all other circumstances being the same ; though it is plain 

 that their actual fertility will depend ultimately upon the quantity 

 of rain that falls, because the quantity suited to a wet soil cannot 

 be the same that is suited to a dry one. And hence it often 

 happens that the ingredients of the soil do not correspond to the 

 character of the climate. Silica exists in the soil under the 

 modification of sand, and alumine under the modification of clay. 

 But the one or the other is often to be met- with in excess or 

 defect. Soils in which the sand preponderates retain the least 

 moisture ; and soils in which the clay preponderates retain the 

 most ; the former are dry soils, the latter are wet ones. But it 

 may happen that neither of them is sufficiently favorable to culture ; 

 in which case, their peculiar defect or excess must be supplied 

 or retrenched before they can be brought to a state of fertility. 



In the present state of chemical science, Dr. Ure observes, no 

 certain system can be devised for the improvement of lands, 

 independently of experiment ; but there are few cases in which 

 the labor of analytical trials will not be amply repaid by the 

 certainty with which they denote the best methods of melioration; 

 and this will particularly happen, when the defect of composition 

 is found in the proportions of the primitive earths. In supplying 

 organic matter, a temporary food only is provided for plants, 

 which is in all cases exhausted by means of a certain number of 

 crops ; but when a soil is rendered of the best possible constitution 

 and texture, with regard to its earthy parts, its fertility may be 

 considered as permanently established. It becomes capable of 



