GUANO (derived from the Peruvian word huano, dung) is the excrementitious deposit of certain sea-fowl, which occurred in immense quantities on certain coasts and islands where the eltinate is dry and free from rain. Although the use of guano as a manure is comparatively recent in this country and in Europe, its value in agriculture was well known to the Peruvians long before they were visited by the Spaniards. We learn from the Memoriales Reales of Garcilaso de la Vega, published in 1G09, that in the times of the Incas no one was allowed, under pain of death, to visit the guano islands during the breeding season, or, under any circumstances, to kill the birds which yield this sub stance; and that overseers were appointed by the government to take charge of the guano districts, and to assign to each claimant his due share of the precious material. Alexander von Humboldt first brought specimens of guano to Europe in 1804, and sent them to Foureroy, Vauquelin, and Illaproth, the best analytical chemists of the day.
Mr. Nesbit, in a useful little pamphlet entitled The history and Properties of the Diferent Varieties of Natural Guano, remarks that the quality and value of these manures, commercially, depend almost wholly upon the amount of decomposition to which they have been subjected by the action of the atmosphere. The ftecal matter of the fish-eating birds, which, by its long accumulation, forms the guano deposits, consists essentially of nitrogenous and phosphatic compounds, the former being chiefly ammonia salts derived from the decomposition. of the uric acid and orates which exist in the fresh excrements of these birds. The ammoniacal portion of these deposits, and some of the phosphates, are tolerably soluble in water, and are readily washed away by rain. The late prof. Johnston remarked, that " a single day of English rain would dissolve out and carry into the sea a considerable portion of one of the largest accumulations, and that a single year of English weather would cause many of them entirely to disappear." In
dry climates, where very little rain falls, as in some parts of Bolivia and Peru, on the western coast of South America, the dung deposited suffers very little from the action of the atmosphere, and retains nearly the whole of its soluble nitrogenous and phosphatic compounds. Guanos, on the other hand, found in regions where rain falls freely, lose a great part of their soluble constituents, but remain rich in their less soluble constitu ents—the phosphates of lime and magnesia. Mr. Nesbit divides guanos according to their composition, into three classes: 1. Those which have suffered little by atmos pheric action, and which retain nearly the whole of their original constituents, such as the Augamos and Peruvian guanos. 2. Those which have lost a considerable portion of their soluble constituents, such as the Ichaboe, Bolivian, and Chilian guanos. 3. Those which have lost nearly all their ammonia, and contain but little more than the earthy phosphates of the animal deposit. Many of these are largely contaminated with s:tad. In this class we place the various African guanos (excepting that from Ieliaboe), West Indian guano, Koaria Mooria (islands off the coast of Arabia) guano, Sombrero guano, Patagonian guano, Shark's bay guano (from Australia), etc.
Most of the so-called Peruvian guano has been obtained from the Chincha islands, which are three in number, and are situated about 12 in. off the coast of Peru, between 13 and 14 degrees s. lat. Each of these islands is from 5 to 6 m. in circumference, and consists of granite covered with guano, in some places to a height of 200 ft., in succes sive horizontal strata, varying in thickness from 3 in, to a foot, and in color from a light to a dark brown. Sometimes, however, is found a vertical surface of upwards of 100 ft. of a perfectly uniform appearance. If Htimboldt's statement is correct. that " during 300 years the coast-birds have deposited guano only a few lines in thickness," toe extreme age of the lower strata becomes at once obvious.