286 JUNES 



of silver (stephanite and polybasite), muriate of silver (horn silver), and grey copper. 

 Many explorations are cjirried on in certain earthy ores, called colorados, similar 

 to the pacos of Peru. Lastly, there are ores of other metals, which are worked 

 principally, and sometimes exclusively, for the silver which they contain ; such aro 

 the argentiferous sulphides of lead, of copper, and of iron. 



Ores of very great richness occur in Mexico ; but the average is only from 3 to 4 

 ounces per cwt, or from 18 to 25 in 10,000. There are some, indeed, whose estimate 

 does not exceed 2 ounces. Almost all the argentiferous veins afford a little gold ; 

 the silver of Guauaxuato, for example, contains j. The enormous product of the 

 Mexican mines is to be ascribed rather to the great facility of working them, and the 

 abundance of ores, than to their intrinsic richness. The present yield is estimated at 

 above 5,000,0002. for silver, and 62,000^. for gold. 



The art of mining was little advanced in this country at the period of Humboldt's 

 journey ; the workings presented a combination of small mines, each of which had only 

 one aperture above, without any lateral communications between the different shafts. 



The form of these explorations was too irregular to admit of their being called 

 regular slopes. The shafts and the galleries were much too wide. The interior 

 transport of the ores is generally effected on the backs of men ; rarely by mules. The 

 machines for raising the ore and drawing the water are in general ill-combined, and 

 the horse-whims for setting them in motion ill-constructed. The timbering of the 

 shafts is very imperfectly executed ; the walled portions alone are well done. There 

 are some adit-levels, but they are too few, and ill directed. The efforts of the 

 English companies have produced but little change either in the mining or subsequent 

 treatment of the ores. 



The silver ores of Spanish America are treated partly by fusion and partly by amal- 

 gamation, but more frequently by the latter mode ; hence the importation of mercury 

 forms there an object of the highest importance, especially since the quicksilver mine 

 of Huancavelica fell in, and ceased to be worked on the same scale as previously. 



Gold mining is carried on in Nicaragua, and some gold is also yielded by Costa 

 Rica, and the Island of Aruba. 



The most important of these gold-sands are washed on the western slope of the 

 Cordilleras, viz. : in New Granada, from the province of Barbacoas to the Isthmus 

 of Panama, and to Chili. There are likewise some on the eastern slope of the Cor- 

 dilleras, in the high valley of the river Amazons. The washings of New Granada 

 produce, also, some platinum. 



The mines, properly so called, and the washings of South America, furnish, altogether, 

 42,575 marcs, or 10,418 kilogrammes (22,920 Ibs. Eng.) of gold, worth 1,435,720^. 



Besides the extensive washings of the sands that produce the, diamonds and other 

 precious stones, the platinum, and a great part of the gold of Brazil, mines of 

 gold, lead, and iron aro opened in what appear to be ancient geological formations, 

 very different from those of the Cordilleras. There are no silver mines, and this, 

 again, indicates a great difference between the deposits of Brazil and those of 

 Spanish America. The province of Minas-Geraes in Brazil is that most remarkable 

 for its mineral productions. The slaty strata of the country contain intercalated 

 portions of qiiartzose rock, among which a micaceous one, called Itacolumite, and one 

 largely charged with scales of. specular iron, termed Jacotinga, are regarded as con- 

 stant accompaniments of the gold. 



Several English companies have for years worked gold mines in this region ; among 

 which that of St. John d'El Bey still yields a considerable profit, due in a great measure 

 to the steady skill and economy with which the underground works, as well as the 

 stamping and dressing of the auriferous ' stone ' is conducted : this is an auriferous 

 pyrites. Among the most noted of the mines are the Bahu, Gongo Soco, and Morro 

 Velho, which although yielding only from two to three oitavas (or eighths of an ounce) 

 per ton, are worked on a large scale. The Morro Velho, which was the largest gold 

 mine in Brazil, is now suffering from the effects of a most disastrous fire which oc- 

 curred there a few years ago. Among other interesting minerals, the rare metal 

 palladium is found mingled with some of the Brazilian gold, and it was owing to the 

 liberality of the well-known assayer, Percival Johnson, F.R.S., that the Geological 

 Society of London was for years enabled to bestow an annual ' Wollaston ' medal struck 

 in palladium, of which that chemist was the discoverer. 



MIXES OF NOETH AMERICA. 



Within the last few years a stupendous activity in the production of certain metals 

 has succeeded to the unimportant trials which at intervals used to be made. It was 

 especially the discovery of gold in California in 1848. which invited the attention of 

 the world to the metallic riches of the Pacific side of this continent, or to the western 



