2 Geological and Miscellaneous Notice of Tarapaca. 



of sulphurous vapor. Parts of this plain afford support to coarse 

 grass and bushes ; one kind of Cactus grows rankly, attaining 

 the height of eighteen or twenty feet, and a foot or more in di- 

 ameter. It is collected by the inhabitants, and being split, serves 

 for doors and rafters to their houses. 



The range of mountains bounding this inclined plain on the 

 west, and separating it from the great parnpa, or plain, of Tama- 

 rugal, is composed of sandstone, with beds of gypsum, and is 

 intersected by deep and abrupt ravines, some of which extend to 

 the sea, while others terminate on the eastern border of the plain. 

 The range of mountains on the western side of the pampa of 

 Tamarugai is composed of feldspar-porphyry, resting on granite. 

 The base at the west, in many places, is washed by the Pacific 

 Ocean ; but in parts of the coast, as at Iquique, a plain of seve- 

 ral square leagues intervenes, composed of shells adhering together 



and of the same species as now exist in great numbers on the 



shore. The greater portion of these shells are partially decom- 

 posed, and may be easily crumbled to powder, while many of 

 them are perfect and bear no marks of abrasion. Inland toward 

 the mountains they form a compact uniform bed, scarcely a trace 



of the original shells being discernible, and as we approach the 



shore the forms become gradually more distinct till we meet with 

 the living shells on the coast. Near the mountains the plain is 



covered with fine siliceous sand, the position of which is con- 

 stantly shifting by the wind, forming hills of considerable eleva- 

 tion, and presenting a great variety of beautiful plains and curves. 



The pampa of Tamarugai, lying between the two ranges of 



mountains before mentioned, is from three thousand to three 

 thousand five hundred feet above the level of the sea. At the 

 north it is bounded by a similar plain of greater elevation, and 

 at the south by a deep and broad quebrada, through which runs 

 an inconsiderable river, called the Loa. The surface presents 

 clay, sand, gypsum, and common salt, mixed with nitrate and 

 sulphate of soda. The three former substances, separately, cover 



large tracts of country, as do also the latter, united in various 



proportions, and nearly free from earthy matter. In some parts 

 of the parnpa, particularly at the south and east, the beds of clay 

 are many miles in extent, and present a surface uniformly smooth 

 and level, and so hard that when riding over it the hoofs of the 

 mules make no impression. On the eastern side, further north, 



