THE NONMETALLIC MINERALS. 



375 



may be readily removed by pick and shovel. The first deposits to be 

 worked are stated by Penrose to have been those of the Chincha 

 Islands, off the Peruvian coast. These were practically exhausted 

 as early as 1872. Other islands which have been worked and com- 

 pletely if not entirely stripped are those of Macabi, Guanape, Bal- 

 lestas, Lobos, Foca, Pabellon de Pica, Tortuga, and Huanillos. 



A mean of 21 analyses of Macabi Island guano, by Barral, ?s quoted 

 by Penrose, 1 showed: 



Nitrogen -. 10. 90 



Phosphates 27. 60 



Potash 2 to 3 



Other analyses are given in the following table: 



a Containing sometimes very considerable quantities of phosphates of alumina and the oxide of 

 iron. 



Aside from on the islands, guano is found all along the coast of the 

 Chilean province, of Tarapaca, from Carmarones Bay to the mouth of 

 the river Loa, there being scarcely a prominence or rock on the shore 

 that does not contain some guano. According to the Journal of the 

 Society of Chemical Industry, 2 the deposits have been known from a 

 very early date. The aborigines of the valleys and gullies of Tarapaca, 

 Mamina, Huatacondo, Camina, and Quisma were acquainted with the 

 fertilizing qualities of guano, and they conveyed it from the coast to 

 their farms on the backs of llamas. 



The southern beds vary so much in aspect and color that it fre- 

 quently requires an experienced eye to make them out. Many of the 

 deposits are covered with immense layers of sand, while others are 

 buried beneath a solid layer of conglomerate. Guano is also fre- 

 quently found in the fissures and gullies which descend to the sea- 



1 Bulletin No. 46 of the United States Geological Survey. 

 * Volume VI, 1887, p. 228. 



