Note 127 — XXII.

"Peru; Sketches of Travel, 1839-42, by J. J. v. Tschudi." St. Gall, 1846: Vol. i. p. 335. Also, "Investigations on the Fauna of Peru." St. Gall, 1844-46. The author from personal observation speaks as follows of these singular sand-columns, whirling along before the wind. "Driving before a strong wind, the medanos speedily overleap all barriers, the lighter and more easily-propelled preceding the heavier like an advanced guard. Sometimes they are hurled against each other, when, so soon as they meet, they are dashed violently together, and break up simultaneously. Frequently a flat stretch of ground is covered within a few hours by a row of sand-hills, which within a day or two more resume their level monotonous appearance. The most experienced guides consequently become confused as to the way, and it is they who the soonest give way to despair as they wander blindly about among the sand-hills. The small mountain-spurs, by which the country is traversed from W. to E., afford some sort of clue, but these oases are few and far between in the sterile wilderness around."