T]ic 3Ied(mos, or moveable Sand-hills. 351 



appearance as they spin along before a S. E. wind, admirably 

 described by Tscliudi in his valuable Sketches of Travel in 

 Peru. These extraordinary pillars, which constantly change 

 both their form and position, and complete the perplexity of 

 the traveller, are usually semi-circular, 8 or 10 feet high, 

 and from 20 to 50 feet wide, but occasionally they are seen 

 50 feet in height, when their diameter is about 150 feet. 

 They are of most frequent occurrence in the hot season, 

 when the parched sand obeys the slightest impulse of the 

 atmosphere, whereas in winter, owing to the deposition of 

 a fine penetrating dew [gama), which all along the coast of 

 Peru supplies the place of rain, which is never seen, the sand 

 increases in weight, and the basis of the column is solidified, 

 so to sjDeak, by the moisture absorbed. Between Port d'ls- 

 lay and Arequipa, the medanos are first encountered about 

 18 miles inland, or nearly half way across the sand-barren. 



In the dells near the harbour volcanic ashes are occasion- 

 ally found at certain spots, whereas they are never dis- 

 covered further inland, nor near the volcano of Arequipa, 

 which since the memory of man has never been known to be 

 in a state of activity, and whose beautiful cone, not unlike 

 that of Ometepec in Nicaragua, seems to be densely wooded 

 up to the very summit. Apparently these are the remains 

 of former eruptions of a neighbouring volcano, which have 



from W. to E., afford some sort of clue, but these oases are few and far between in 

 the sterile wilderness around." 



