64 SCIENTIFIC AGRICULTURE. 



141. .On these Peruvian islands it seldom or never 

 rains, while the hot sun rapidly evaporates the mois- 

 ture naturally contained in the deposit, and leaves 

 the valuable constituents in their most concentrated 

 form. On other islands frequented by sea-birds, a 

 great deal of that which is valuable in the deposits is 

 washed out by rains more or less frequent. Guano 

 has been brought from a few islands on the coast of 

 Africa and other parts of the world where rain sel- 

 dom falls, but none has been found equal in value to 

 the Peruvian. 



142. The guano-producing birds feed on fish, a 

 food especially rich in phosphates and nitrogenous 

 compounds. The mixture of their solid and liquid 

 excrements contains in a highly concentrated form 

 those very elements which are most likely to be 

 deficient in soils, and hence its universal applica- 

 bility. 



143. The composition of guano varies consider- 

 ably in different samples. An average analysis of 

 Peruvian guano imported into Ireland in 1876 is 

 given by Johnston and Cameron as follows : 



Per cent. 



Moisture 13.13 



Organic matter, etc.* 48.17 



Calcium phosphate 26.58 



Alkaline salts i i.oo 



Insoluble matter - 1.12 



100.00 



* Yielding ammonia II. 80. 



