6 R. A. F. PENROSE, JR. 



also to special parts of it, either large or small. Thus the term 

 Tamarugal Pampa applies to a large part of the basin of Tarapaca 

 and northern Antofagasta, while the term Tarapaca Pampa applies 

 only to the part of the basin region in the province of that name; 

 and the terms Huara Pampa, El Toco Pampa, Taltal Pampa, and 

 many others apply to purely local districts. 



Rain is very rare in the pampa, frequently three or four years, and 

 sometimes eight or ten years of unbroken drought occurring. The 

 Coast Range in this part of Chile is almost as dry as the pampa, though 

 fogs from the ocean are common, and their moistening influence 

 encourages the growth of a little grass and a few cacti on the tops 

 of the hills. Even the fogs, however, rarely reach the pampa. 

 Many streams flow westward from the Andes, but most of them 

 rapidly -evaporate or sink below the surface when they come to the 

 pampa, and hence a map of the region shows them suddenly termi- 

 nating at the foot of the mountains (see map, Fig. i). The waters 

 that sink continue westward underground, occasionally rising near 

 enough to the surface to form oases in the desert, and then disappear- 

 ing again. In times of high water, some streams reach the sea on 

 the surface, but only very few do so perennially. Sometimes during 

 seasons of great rises in the rivers of the Andes, the pampa is flooded 

 over large areas. Such occurrences are rare, though some have been 

 recorded, and evidence of them is seen in the dry gullies running across 

 the pampa and in the local accumulations of drift wood from the Andes. 

 In past ages these floods were probably more frequent than now, but 

 the normal condition of the pampa today is one of great aridity. 

 The very presence of nitrate deposits is evidence of the extreme 

 dryness of the region, for nitrate is easily soluble, and water would 

 soon dissolve it and carry it away. The only vegetation is in a few 

 isolated spots where underground streams rise near enough to the 

 surface to support the growth of a little grass or a few stunted trees. 

 Elsewhere the pampa is a sandy desert, from which an impalpable 

 dust rises in blinding clouds with the slightest wind and where the 

 drifting sands form immense dunes similar to those seen on the 

 coast. 



The surface of the pampa is composed mostly of sand, clay, and 

 gravel, with masses of more or less rounded rock fragments scattered 



