372 



AGRICULTURE. 



to be hoped, may be formed by a trigonometrical 

 survey of the whole Union. This would give em- 

 ployment to an army of civil engineers who are 

 now reposing in idleness, and prove a vast field of 

 industrious employment, the results of which would 

 be alike useful and honourable to the nation. 



AGRICULTURE. 



The intimate connexion of geology with agricul- 

 ture must strike the most superficial observer. On 

 this subject, the following remarks of Mr. Bakeu^ell 

 are well worthy of attention : By a wise provision 

 of the Author of Nature, it is ordained that those 

 rocks which decompose rapidly are those which 

 form the most fertile soils ; for the quality of soils 

 depends on the nature of the rocks from which they 

 were formed. Granite and silicious rocks form 

 barren and sandy soils ; argillaceous rocks form 

 stiff clay ; and calcareous rocks, when mixed with 

 clays, form marl; but, when not covered by other 

 strata, they support a short but nutritious vegeta- 

 tion. For the formation of productive soils, an in- 

 termixture of the three earths, clay, sand, and lime, 

 is absolutely necessary. The oxide of iron also 

 appears to be a requisite ingredient. The propor- 

 tion necessary for the formation of a good soil de- 

 \pends much on the nature of the climate, but more 

 on the quality of the subsoil, and its power of re- 

 taining or absorbing moisture. This alone may 

 make a soil barren, which, upon a different subsoil, 

 would be exceedingly productive. When this is the 

 case, either drainage or irrigation offers the only 

 means of permanent improvement." Again he re- 

 marks, that, " in proportion as soils possess a due 

 degree of tenacity, and power of retaining or ab- 

 sorbing heat and moisture, the necessity for a sup- 

 ply of manure is diminished, and in some instan- 

 ces the earths are so fortunately combined as to 

 render all supply of artificial manure unnecessary 



