174 GUANO. 



guano," might be admitted as a good intermediate 

 variety. 



The best guano comes from the rainless region 

 of Peru, which lies beneath the 5th and 20th degree 

 of south latitude. Here it covers the rocky surface 

 of the cliffs and islands in layers of very various 

 thickness, in a similar way to our own clay strata. 

 The depth or thickness of these layers varies from 

 one or a few yards to twenty and thirty, and some- 

 times even more. In the first year in which a layer 

 of guano is deposited it has a white color, and is 

 called guano bianco ; this is generally acknowledged 

 to be the best, and is bought from the Peruvians, 

 who esteem it highly, at double the price which is 

 given for the brown. It possesses nearly the same 

 constituents, and produces the same effects, as our 

 pigeon-manure ; but its action is still more energetic, 

 because it is richer in azotized substances. The 

 reason of this difference consists in the difference of 

 food. The marine birds, whose excrements furnish 

 guano, live upon fishes, whilst our pigeons take only 

 vegetable nourishment ; an animal diet is always 

 richer in nitrogen, and furnishes for this reason a 

 manure that abounds more in this element than one 

 furnished by a vegetable diet. The layers which suc- 

 ceed to the white have a light grayish-brown color > 

 still deeper down, they become darker, and at the low- 

 est part rust-colored ; the lower layers, moreover, are 

 invariably more compact than the upper. It is evi- 

 dent that the inferior layers are the oldest ; putrid de- 



