( 41 ) 



is owing either to the sample having been ta- 

 ken from different strata, or else to the trans- 

 formation of the urateof ammonia, of some of 

 them, into carbonate of ammonia, which is 

 very volatile. 



The cost of guano in this country, varies 

 from twenty-five to forty dollars per ton, ac- 

 cording to quality. 



Experiments made in France have deter- 

 mined 250 to 500 lbs., as the proper propor- 

 tion per acre. Like colombine it acts ener- 

 getically, and should therefore be used with 

 discretion. The composition of guano con- 

 firms its origin, and moreover the island, 

 which furnishes it still serves as a refuge for a 

 multitude of birds. According to Humboldt's 

 calculations, even supposing the surface of 

 these islands to be covered with the birds, 

 three centuries would be required to form a 

 layer of excrements of 0.3937 inches in thick- 

 ness, and hence we can only conjecture the 

 length of time consumed in the formation of 

 these vast deposits. 



New deposits of guano have been found 

 upon the coasts of Africa, whence it is ex- 

 ported in large quantities. This guano is 

 less nitrogenous than that from Peru. 



