302 



On Guano. 



it is altogether derived from the dung of the countless flocks of 

 sea-fowl which frequent the islands and rocks of the Peruvian 

 shore : yet the evidence on this point is perfectly satisfactory. 

 The living birds still deposit the white guano on the islands to 

 which they resort. In the isles of I slay and Jesus 20 to 25 tons 

 of this recent guano are occasionally collected in a single season. 

 In the island of Torrecilla the white may be seen changing into 

 the red variety (Winterfeldt) ; while, in the midst of the' great 

 accumulations of the latter kind, bones and feathers (Frezier) of 

 birds are found, as if to remove any doubt which might still 

 remain as to its origin. Its real origin, indeed, was well known 

 to the government of the Incas, and its national importance fully 

 understood. It was made a capital offence to kill the young 

 birds on the guano islands. Each island had its overseer ; and, 

 as the whole coast from Arica to Chaucay, a distance of 200 

 leagues, was manured almost entirely with guano, eact island was 

 assigned to a special district of the main land, and its produce 

 was conveyed to that district alone (Humboldt). 



It was not till the arrival of the Spaniards that the original source 

 of the guano was for a time doubted ; yet, when we consider how 

 great a lapse of time it must have required to admit of the accu- 

 nmlation of the extensive beds of ancient guano still known to 

 exist, we cannot wonder that early European visitors should have 

 received with hesitation what we now readily admit as the true 

 account of its origin. Of late years the increase of traffic on the 

 coasts has disturbed or driven away the birds, and thus materially 

 diminished in many localities the annual produce of the white or 

 recent guano. Since the opening of the port of I slay the birds 

 have nearly deserted the adjacent inlets" (Winterfeldt). 



It may be further added on this point that the chemical con- 

 stitution of guano has been found to be exactly such as is to be 

 expected from the above account of the mode of its production. 



Why, it may be asked, does this substance accumulate within the 

 eight degrees of latitude above stated only, though the sea- fowl 

 are said equally to abound beyond these limits ? This question 

 involves a consideration both of the chemical nature of the sub- 

 stance itself and of the physical condition of the country in which 

 it accumulates ; it will be more naturally discussed, therefore, in 

 a subsequent section. 



§ 3. Effects of Guano on Vegetation. 

 It is known to have been a common practice to manure with 

 guano as far back, at least, as the twelfth century ; and the possi- 

 bility of raising crops on the sandy plains of Peru is said to depend 

 altogether on the application of this substance* (Humboldt). 



* We have seen bow it was prized by tbe ancient Peruvians. About 



