As soon as the dealers in guano begin to work one of the beds, the island on which it is formed, is abandoned by the birds. It has also been remarked, that since the increase of trade and navigation, they have withdrawn from the islands in the neighborhood of the ports.
Much has recently been written on the employment and utility of guano; but the manner in which it is applied as manure in Peru, seems to be but little known. The Peruvians use it chiefly in the cultivation of maize and potatoes. A few weeks after the seeds begin to shoot, a little hollow is dug round each root, and is filled up with guano, which is afterwards covered with a layer of earth. After the lapse of twelve or fifteen hours, the whole field is laid under water, and is left in that state for some hours. Of the Guano Blanco a less quantity suffices, and the field must be more speedily and abundantly watered, otherwise the roots would be destroyed. The effect of this manure is incredibly rapid. In a few days the growth of a plant is doubled. If the manure be repeated a second time, but in smaller quantity, a rich harvest is certain. At least, the produce will be threefold that which would have been obtained from the unmanured soil.
The haciendas of the valley of Chancay have, during the last fifty years, consumed annually from 33,000 to 36,000 bushels of guano brought from the islands of Chancha and Pisco. The price of the bushel of colored guano is one dollar and a quarter, and the price of the white from two to three dollars. The price has recently undergone many fluctuations, in consequence of the great exports to Europe.
The employment of this kind of manure is very ancient in Peru; and there is authentic evidence of its having been used in the time of the Incas. The white guano was then chiefly found on the islands opposite to Chincha; so that for upwards of 600 years the deposit has been progressively removed from those islands without any apparent decrease of the accumulation. The uniformity of climate on a coast where there is not much rain, must contribute to render the Peruvian guano a more arid manure than the African, as fewer of the saline particles of the former being in solution, they are consequently less subject to evaporation.
From 3° 35′ to 21° 48′ south latitude, a plain of sand, 540 leagues long, and varying from 3 to 20 leagues in breadth, stretches along the coast of the Pacific Ocean. It is intersected by chains of small hillocks, which, extending westward from the Cordilleras, gradually diminish in height, and either become blended with the plain, or form abrupt promontories, which project into the sea. Between the river Loa, which marks the southern frontier of the Peruvian coast, and the Tumbez, on the northern boundary, fifty-nine rivers, great and small, pass through the line of coast. Proceeding from the avalanches of the Andes or the small alpine lakes, they force their way through narrow mountain-valleys, irrigate the waste grounds, and then, after brief courses, flow into the great ocean.
A fine light yellow drift sand covers hill and dale. It is only where rivers intersect the plain that oases of luxuriant vegetation are formed. The peril of traversing these plains is greatly increased by the movability of the sand and the Medanos. The strong winds raise immense clouds of dust and sand. The sand rises in columns of from eighty to a hundred feet high, which whirl about in all directions, as if moved by magic. Sometimes they suddenly overshadow the traveller, who only escapes from them by rapid riding.
The medanos are hillock-like elevations of sand, some having a firm, others a loose base. The former, which are always crescent-shaped, are from ten to twenty feet high, and have an acute crest. The inner side is perpendicular, and the outer or bow side forms an angle with a steep inclination downward. When driven by violent winds, the medanos pass rapidly over the plains. The smaller and lighter ones move quickly forwards before the larger ones; but the latter soon overtake and crush them, whilst they are themselves shivered by the collision. These medanos assume all sorts of extraordinary figures, and sometimes move along the plain in rows forming most intricate labyrinths, whereby what might otherwise be visible in the distance is withdrawn from the view of the traveller. A plain often appears to be covered with a row of medanos, and some days afterwards it is again restored to its level and uniform aspect. Persons who have the greatest experience of the coast are apt to mistake their way, when they encounter these sand-hills.
The medanos with immovable bases are formed on the blocks of rock which are scattered about the plain. The sand is driven against them by the wind, and as soon as it reaches the top point it descends on the other side until that is likewise covered; thus gradually arises a conical-formed hill. Entire hillock-chain with acute crests are formed in a similar manner. The small hillock-chain, by which the coast is intersected obliquely from east to west, is a boundary which arrests the progress of the wandering medanos; otherwise fruitful oases would soon be converted into barren sand-flats. A correct observation of these hillock-chains affords a most certain scale for ascertaining the direction of the prevailing wind. On their southern declivities are found vast masses of sand drifted thither by the mid-day gales. The northern declivity, though not steeper than the southern, is only sparingly covered with sand. If a hillock-chain somewhat distant from the sea extends in a line parallel with the Andes, namely from S.S.E. to N.N.W., the western declivity is almost entirely free of sand, as it is driven to the plain below by the southeast wind, which constantly alternates with the wind from the south.
The movements and new formations in the deserts (like restorations from death to life) are only in full activity during the hot season; for then the parched sand yields to the slightest pressure of the atmosphere. In the cold season its weight increases by the absorption of humidity. The particles unite in masses, and more easily resist the wind. In the meantime the hillocks also acquire more firmness or compression by the increased weight which presses on them from above.
In November, summer commences. The rays of the sun are refracted on the light grey sandy carpet, and are reflected back with scorching power. Every living thing which does not quickly escape from their influence is devoted to certain destruction. No plant takes root in the burning soil, and no animal finds food on the arid lifeless surface. No bird, no insect moves in the burning atmosphere. Only in the very loftiest regions, the king of the air, the majestic condor, may be seen floating, with daring wing, on his way to the sea coast. Only where the ocean and the desert blend with each other is there life and movement. Flocks of carrion crows swarm over the dead remains of marine animals scattered along the shore. Otters and seals impart life to the inaccessible rocks; hosts of coast birds eagerly pounce on the fish and mollusca cast on shore; variegated lizards sport on the sand hillocks; and busy crabs and sea spiders work their way by furrows through the humid coast.