Page:The American Cyclopædia (1879) Volume I.djvu/511

ANDES 479 from the eastern slopes on which it is precipi- tated, eastward toward the Atlantic, feeding the great rivers of the continent, and spreading fer- tility along their paths. Glaciers are rare, being found only in the narrow ravines of the southern section. The volcanoes of the Andes, 51 in number, are remarkable for their continu- ity, in scattered groups, from the western coast of Patagonia, in lat. 43 28' S., to the northern limits of the Andes a few degrees from the equator ; and even into Central America the continuation of this volcanic belt may be traced in the cordilleras of Costa Kica, Nicaragua, Honduras', and Mexico. The most southern group extends from Yanteles, opposite the island of Chiloe, to Coquimbo, in lat. 30. There is then a space of more than eight degrees of latitude with no volcano known to have been in action, to which succeeds the range of vol- canoes of Bolivia and Peru, the extent of which is from lat. 21 to 15 S. Thence to the vol- canoes of Quito is a district of fourteen degrees of latitude, little known and thinly populated. No volcanoes are spoken of in it, but they may be there and have escaped the observation of civilized man. The volcanoes of Quito extend from 100 m. S. of the equator to 130 m. N. of it ; and from their northern termination it is about six degrees further to the southern termination of the volcanoes of Central America. They are not only remarkable for the long line of coun- try they spread over, but also for the great height of many of the peaks, and their extreme- ly destructive character. The products of an eruption are usually water, mud, ashes, and fragments of pumice, trachyte, and porphyry. But the volcanoes of the Andes are singularly exempt from floods of lava. From high up the flanks of Antuco in Chili, the summit of which rises 16,000 feet above the sea, immense cur- rents of lava flowed in 1828 ; but this is a rare occurrence, the matters usually ejected being vapors and scoriae. The outbursts of the vol- canoes are closely connected with the frequent and disastrous earthquakes of this region. These commotions appear to extend under the whole range of the Andes, and even far out under the ocean. So frequent are they that M. Boussingault is of opinion that a full regis- ter of them would show that they are inces- sant. The geological structure of the Andes shows that the chain was slowly upheaved in mass from the sea, and has since undergone three subsidences. Indeed, there are evidences that the Andes are now subsiding again, for successive measurements indicate a lower ele- vation. (See "American Journal of Science," October, 1871, p. 267.) In the pass of Uspa- llata, the two parallel ridges, based on the an- cient porphyries, are capped, the range next the coast with black clay slates containing the grypheas, ammonites, and other fossil shells of Jurassic and cretaceous age, and altered by in- trusion of the igneous rocks ; while the eastern range is covered with still later formations, as sandstones and conglomerates made up of the fragments of the rocks of the western range, and bearing all the appearance of the tertiary strata found along the Pacific coast. These later for- mations also are intermingled with trap rocks and volcanic tuffs, and altered by contact with the granitic rocks, which since the deposition of the sedimentary rocks have intruded among the strata. The metallic veins from the gran- ite also penetrate them, and veins of gold have been worked in close proximity to fossil trunks of trees, found by Darwin standing im- bedded in the stratified rocks. The Andes ap- pear throughout their length to carry a similar geological structure, which is made manifest as well by a similarity- of mineral productions as by the reports of those naturalists who have ascended the summits ; granitic and porphyritic rocks form the lower portion, and on these rest immense formations of mica slate, gneiss, and quartz rock. Upon the very summits are found the tertiary strata, which, like the same forma- tion extending along the Pacific coast, are pro- ductive in beds of bituminous coal, and the va- riety called brown coal, at intervals from Pata- gonia to Panama. Beds of this coal are worked in Chili for the use of steamships ; and in the mining region of Pasco in Peru, in the imme- diate vicinity of its celebrated silver mines, and at an elevation of over 14,000 feet, coal prob- ably of the same age is found in abundance. The quality of such coal is not likely to be as good as of the bituminous coals of the true coal formation, but our data are very imperfect on this point, as also whether the real carbonif- erous rocks are found at all in South America. The secondary rocks generally cover the gran- ite in the mountains of Venezuela, but thin away toward the equator ; and in the plains of the Eio Negro Humboldt noticed the bare granite in patches of 10,000 square yards forming the level surface. Mines of silver have frequently been alluded to in describ- ing different localities along the Andes. Near the equator and N. of it they are not produc- tive ; but in Peru and Bolivia they are prob- ably unsurpassed in richness by any mines of this metal in the world. The mines of cinna- bar of Huanca Velica, in southern Peru, have in former times produced very large quantities of mercury, and the same ore is also found near Tarma in the valley of the Jauja river, and in the equatorial Andes, N. W. of Cuenca; platinum is met with in small grains in the al- luvium near the Pacific coast of New Granada. Gold is found in the silver veins of Peru, and is worked in veins in Chili. In Bolivia it- is washed from the deposits along the streams. Lead ores are common with those of silver, but are not regarded as of much value. The copper mines of Chili are very productive in the rich oxides and carbonates of this metal. Many cargoes of these valuable ores are ship- ped every year to Swansea in Wales to mix with the lean ores of Cornwall ; and our own copper-smelting establishments along the coast receive occasional supplies from the same