APPENDIX 



493 



collecting the weeds and Francis Masson (1777-8) was enriching the 

 gardens at Kew with the indigenous trees and shrubs of these islands 

 (Aiton's Hortus Kewensis, 1789). Yet if man's interest is more 

 attracted by the second, the history of our race is intimately bound 

 up with the first, and weeds offer from this standpoint almost virgin 

 ground for the investigator. 



Note 34. 



Observations on the medanos or moving sand-hills of the Ancon 

 coast region in Peru. (General remarks on this subject will be 

 found on p. 271). 



The following observations were made in February 1894 in the 

 Ancon district north of Callao. Broad, sandy, and almost barren 

 plains extend inland from the shores of Ancon Bay for about three 

 miles to the foot of the mountains, rising in that distance 200 to 300 

 feet, the sand on the plains being only a foot or two in depth. A 

 sand-covered spur of the mountains descends to the coast on the 

 south side of the Ancon plains, having an elevation opposite the 

 town of 400 feet. Immediately south of the spur is a large sandy 

 beach, the Playa Mayor, more than a mile in length, which was the 

 starting-place of a line of medanos that at the time of my visit took 

 an oblique north-easterly course before the prevailing south-west 

 winds of four and a half to five miles to the base of the inland range 

 of mountains. The whole of the region here concerned up to an 

 elevation of 500 feet was only a sandy waste, where a tumble-weed 

 of the genus Tillandsia alone found a home. 



As typically displayed, these sand-hills are crescentic in form, 

 twenty-five to thirty feet across, and six to ten feet high, the con- 

 cavity being in front. That they are ever advancing was indicated 

 by the way in which they lay astride the beaten tracks. I observed 

 these medanos after they had reached in irregular order the top of 

 the spur overlooking the Ancon plains. One was perched on the 

 crest at an elevation of 200 feet above the beach, another on the 

 crest at 300 feet, and a third at 360 feet. Before a light wind with 

 a force of about three the sand was steadily moving across the crest, 

 the heavier particles along the surface and the lighter blown through 

 the air. In ten minutes, sand of the weight of 108 grains was blown 

 into the mouth of a round tube, an inch in diameter, that had been 

 placed on the surface. I felt a light rain of sand on my face as I 

 sat watching, and when the wind freshened for a few moments my 

 face was " peppered " with sand. All the sand of the surface was 

 in motion on the crest, both on the medanos and in the spaces 

 between them. I noticed that after the medanos had crossed the 

 ridge they re-formed in an irregular fashion on the descending 

 slopes, unless the descent was steep, when the sand formed a con- 

 tinuous slide. On reaching the plains, 200 to 350 feet below, the 

 medanos resumed their typical shape and gathered into line, or 

 rather into column, for the traverse of the plains. Arranged two 

 or three irregularly abreast in a column about 100 paces in width, 



