MINERALS OF CHILE. 57 



no mines are found higher than four thousand five hundred 

 feet above the level of the sea ; and this peculiarity I believe 

 pertains to all parts of Chile. 



Taking the Bay of Copiapo as a starting-point and going 

 east, we find the underlying rock of the country granite, the 

 surface being covered with tertiary deposits of very modern 

 origin, the same that is found at the mouth of all the Chilean 

 rivers. These deposits form two and three terraces, and con- 

 sist principally of sand mixed with shell and gravel. At 

 about six miles from the sea solid calcareous beds show them- 

 selves, containing species of crustaceas now found living on the 

 shore. The granite of this coast is fine-grained, having the 

 same aspect as that in the neighborhood of Coquimbo, and is 

 the same as that of the mountains of Carrisal, San Juan, and 

 La -Higuera, celebrated for their copper-mines. Granite-hills 

 project frequently above the tertiary planes that extend to and 

 rest on the first chain of granite-rocks which are low and 

 rounded. It is in these rocks wherever seen, whether on the 

 coast or projecting above the tertiary planes, or, when still 

 further east, projecting through secondary strata, that the 

 copper and gold are found. A good example of this is the 

 Cerro del Cobre mountain, which elevates itself at the bottom 

 of the valley of Copiapo. This mountain is composed of an 

 elevated mass of porphyritic diorite, traversed by veins of iron 

 and copper ores, containing considerable quantities of magnetic 

 iron and ferruginous oxide of copper, copper pyrites, etc. It 

 forms a species of granitic island in the midst of stratified 

 porphyritic and other compact rocks more or less calcareous, 

 and preserves all the characters of the coast rocks, even to the 

 nature of the veins that it contains. 



Further east, overlying the granite and dioritic rocks, are 

 stratified porphyries; and here, at a height of two thousand 

 two hundred and fifty feet above the level of the sea, as at 

 Ladrillos, commence the indications of silver, disseminated in 

 extremely fine particles of chloro-bromide ; but on excavating 

 this indication soon disappears, and it is not until we reach 

 a more elevated point that silver is found very abundantly, 

 and where the stratification becomes more perfect. Above the 

 stratified porphyries there are calcareous and schistose rocks, 

 more or less disturbed from their original position. 



