62 SCIENTIFIC AGRICULTURE. 



verization of the soil and a systematic application of 

 fertilizers. 



137. The fertilizer in common use among the Pe- 

 ruvians was guano, the excrement of immense flocks 

 of sea-birds which frequent the rocky islands near the 

 coast. Countless numbers of birds have for centu- 

 ries hatched and reared their young on these islands, 

 leaving deposits which cover a large extent of sur- 

 face, and are in places from twenty to fifty feet in 

 thickness. It was estimated, thirty years ago, that 

 on the Chincha group of islands there were from 

 twenty to twenty-five millions of tons. It has been 

 so long accumulating that in some localities the de- 

 posit is found in layers with sand like a regular geo- 

 logical formation. 



138. The importance of this fertilizer was so 

 highly appreciated by the old Peruvians that, when 

 the Spaniards first visited the country, special laws 

 were in operation to regulate its use, and enforce its 

 application to the soil by those engaged in agricul- 

 ture. Its value was not known or appreciated in 

 Europe or in our own country until within the last 

 thirty or forty years. The credit of introducing it 

 into Europe is ascribed to Humboldt. The first 

 cargo was taken to England in 1826, but its value 

 was not understood until a number of years after- 

 ward. 



139. Liebig, in his " Letters on Modern Agricul- 

 ture," says: "Before 1840, guano had never been 

 used as a manure on a European field. When the first 



