THE CHILIAN NITEATE-FtELDS. 435 



genesis of tlie nitrates by tlie disintegration of the felspar rocks exfoliating under 

 the action of the air and changes of temperature, and then transformed to a 

 substance containing kaolin, iron oxide, salts of lime and soda, which in their turn 

 were changed to sodium chlorides and nitrates. But these slow chemical opera- 

 tions can take place only in waterless districts, for wherever the ground is washed 

 by rains or streams the caliche, as the deposit is called, is always melted. Hence, 

 large masses could be formed only on the margin of the basins farthest removed 

 from the Sierra where the running waters had their source. 



In the Pampa de Tamarugal, that is, of the " Tamarisks," the nitrate-fields 

 cover a continuous area of about 500 square miles, with a varjdng thickness, which 

 in some places exceeds 10 feet. According to the calculations of the engineer 

 Smith, the total quantity of nitrates contained in the surface strata of the pampa 

 amounted in 1860 to 65,000,000 tons. Moreover, the presence of extensive 

 underground beds is revealed by numerous fissures in the surface of the ground, 

 which cross each other in all directions. Thus are formed countless polygonal 

 figures covered with small stones, which give to the plain, viewed as a whole, the 

 fantastical aspect of a mosaic pavement. The surface fissures themselves correspond 

 with the underground fissures produced in the nitrate-beds reduced in volume by 

 the crystallising process, and decomposed in prisms analogous to basalt columns. 

 But even these spaces are as nothing to the saline efilorescences deposited by 

 evaporation in the depressions of these arid regions — lacustrine basins of which 

 nothing now remains except the salt. 



Everywhere numerous traces are seen of the presence of water at a former 

 epoch in these arid deserts. The running waters have left their deep beds, whose 

 banks were fringed by a vegetation the remains of which still survive. In the 

 mountainous district stretching between Iquique and Huantajaya explorers have 

 discovered the presence of a vast half-buried forest, whose branches have worn 

 with age, but whose huge stems still exist. As far as can be judged from their 

 appearance, the trees belonged to a species which no longer flourishes either on the 

 coastlands or on the plateau. They were changed to stone, say the Indians, by 

 the god Pachacamac, in order to destroy the wicked generation that dwelt beneath 

 their shade. 



There are evidences of continuous desiccation even since the epoch of the 

 Conquest. In certain now desert districts of Atacama are seen the remains of 

 buildings which no one would now dream of erecting in places rendered absolutely 

 uninhabitable by the absence of water. The very name of " San Fernando de la 

 Selva " given to Copiapo attests plainly enough the presence of an ancient wood 

 (scira) in a climate which is now far too dry for a forest vegetation. It appears 

 also from numerous documents that the Rio Copiapo, at present dry in its lower 

 course, formerly reached the sea. One of the gorges on the east even bears the 

 name of Quchrada Seca (" Dry Ravine "), as if to distinguish it from the channel 

 through which the river flowed seawards. The town of Totoral (" Rushgrove ") 

 perpetuates by its very name the memory of an old fen which still existed at the 

 close of the Spanish rule. 



