In most of the districts porphyry is found with micaceous schists, and the conjunctions of those two rocks with quartz veins is considered an indication of silver. The mode of mining generally is very rude. No mine is accessible by railroad, and few have wagon roads. Usually the reduction works are at a distance from the mines, and the ore is packed on mules. The ore is brought to the surface on the backs of men, up steep inclines, or even up perpendicular shafts, the carriers climbing up on notched poles. In some mines the ore is carried by men to the shaft and there hoisted by whim. There is no mention in Humboldt or Ward of tramways and cars to bring the ore from remote parts of the drift to the shaft. Water is hoisted in the same manner as the ore. Steam was not used previous to the revolution, but it has been coming into use gradually, and now much of the hoisting, pumping, and pulverizing is done by it. The general practice in Mexico as to pulverization has been to mash the ore to a coarse sand under the stamps, and then grind it fine in arrastras. The degree of fineness varies much in the different districts, partly because of differences in the ores and modes of reduction, and partly because of ignorance and prejudice. At Guanajuato the ore is ground to an impalpable powder; at Zacatecas, Catorce, and Fresnillo, in a coarse flour. In 1842, 82 per cent. of the silver yield of Mexico was obtained by the yard amalgamation; 8 per cent. by the Cazo or copper-pan amalgamation, and 10 per cent. by smelting.* In 1800 one-seventh was smelted.t The proportion of smelted silver has been decreasing gradually, and will no doubt continue to decrease. A hundred years ago it was two-fifths of the total yield. Since the opening of the Washoe mines and the successful introduction of the iron-pan amalgamation there, a number of mines have been purchased in Sonora, Sinaloa, Chihuahua, Durango, and Lower California, by Americans, who have introduced machinery and American modes of working, and they would probably have obtained some splendid results, at least in a few instances. before this time, if the civil war had not thrown everything into confusion. The average loss of mercury in the yard amalgamation is a pound and a half to one pound of silver extracted. The best writers on mining in Mexico agree that the country has great wealth as yet undeveloped, and that a time must come when the production of the precious metals will far surpass anything of the past. Humboldt said he was "tempted to believe Europeans have scarcely begun to profit by the inexhaustible fund of wealth contained in the New World. Europe would be inundated with the precious metals if the deposits of ore at Bolanos, Batopilas, Sombrerete, Rosario, Pachuca, Moran, Zultepec, Chihuahua, and so many other places that enjoyed an ancient and just celebrity, were assailed at one and the same time with all the means offered by the perfection to which the art of the miner has attained." The opinion of Ward is given in the following passages: "That the great mineral treasures of Mexico commence exactly at the point where Humboldt rightly states the labors of the Spaniards to have terminated, (above latitude 240,) is a fact now universally admitted by the native miners, although heretofore but little known in Europe. The states of Durango, Sonora, Chihuahua, and Sinaloa contain an infinity of mines hitherto but little known, but holding out, wherever they have been tried, a promise of riches superior to anything that Mexico has yet produced. In common I believe with all those who have had an opportunity of inqniring into the resources of New Spain, I do regard it so well ascertained a fact that her mineral riches are almost unexplored, that I am willing to rest upon it my whole calculation with regard to her future importance as a country.' (Ward, vol. 1, pp. 127–160.) * * * Duport expresses himself thus: "After having visited only Tasco, Real del Monte, and Guanajuato, Humboldt said 40 years ago that there was enough silver in the Mexican mines to flood the world: what would he not have said if he had pushed his researches further north? More strongly convinced than he could possibly be of the abundance of the argentiferous veins, I am not so confident about the brevity of the time within which the progress of science in Europe, and the free intercourse of all nations with Mexico, can exert any considerable influence on the amount of the production of the precious metals."‡ And again he says: "The want of capital, of political quiet, of population, and of education in the northwest of the republic, and of wide-spread scientific knowledge, and finally the high price of mercury, are the obstacles which oppose the increase of the production of the precious metal in Mexico. These causes will exercise their fatal influence for some years yet, and will prevent the yield from passing the figure which it reached at the beginning of this century. But these obstacles are not permanent in their character; they are only temporary, and will after a time be neutralized, and then overcome, by the abundance of the ore and the progress of science, which gives a wider dominion every year to the power of man. The time will come, a century sooner or a century later, when the production of silver will have no limit save that imposed by the steady decrease of its value."§ NORTHERN STATES OF MEXICO.-The late Mr. A. Rémond, whose untimely decease is an irreparable loss to science, made a tour of exploration through the northwestern States of Mexico during the years 1863, 1864, and 1865, in the course of which he carefully examHumboldt, p. 141. ‡ Duport, p. 380. § Duport, p. 426. Duport, p. 369. ined the geology of the country, and collected some valuable statistics on the subject of mines and mining. Professor J. D. Whitney, of the geological survey of California, in March, 1866, submitted to the Academy of Natural Sciences an interesting report from Mr. Rémond. The following extracts convey a clear idea of the geological formation and general characteristics of northern Mexico. The tables accompanying the report show the extent, character, and condition of the mines: "The name of the Sierra Madre' is usually applied to the main range of mountains of this country, or the western border of the plateau which stretches north through the territories of the United States, forming what may be called the great orographical feature of the continent. In northwestern Mexico this crumpled border of the great plateau comprises an extensive mountainous region, by no means forming a continuous single chain, but rather several central ranges, with associated groups of parallel ridges, all having the same general course, which is approximately north-northwest and south-southeast. As the breadth of the chain widens as we go towards the north, so, too, that of the valleys increases in that direction, the whole system of mountains and valleys spreading out in something like a fan shape. "Going north, the chain appears to sink gradually, although determinations of altitude in northern Mexico are extremely few in number. It is certain that there is, in about latitude 320, a depression of the mountain ranges which extends entirely across the continent, and which would enable the traveller to cross from the Atlantic to the Pacific, without necessarily surmounting any elevation greater than 4,000 feet. The southeastern range is the highest, and the culminating point is said to be the Cerro de Cuiteco, 60 leagues northeast of Jesus Maria, on the western borders of Chihuahua. The approximate altitude of the Cumbre de Basascachic is 7,429 feet, and that of Guadalupe y Calvo 7,825 feet. To the north, the ranges east of Sahuaripa are also very high; but they have never been measured. No peaks or ridges, however, in this portion of Mexico attain anything like the elevation of the higher portion of the Sierra Nevada, few if any points exceeding 10,000 feet in altitude. "The direction of the sierra is nearly that of a line connecting some of the best mining districts in Mexico, which are situated on or very near the summit of the mountains. These districts are the following, enumerating them in their geographical order from the south towards the north in Durango, San Antonio de las Ventanas, Guaris amey, and San Dimas, remarkable for their auriferous silver ores, and 62 Mexican leagues northeast of Mazatlan; in Chihuahua, Guadalupe y Calvo and San Pedro de Batopilas, yielding fine specimens of native silver; also, Jesus Maria, in the same State, and the Real del la Cieneguita, Sonora, with silver and gold mines. "GENERAL GEOLOGY.-The geological structure of the occidental slope of the Sierra Madre, as well as that of other parts of this great chain, is exceedingly interesting, and, as yet but very little known, notwithstanding the valuable investigations of Humboldt and other eminent men; for, up to the present time, the age of the different formations has never been fixed with any degree of accuracy, from want of materials and of sufficient observations. In 1863, 1864, and 1865, however, I explored quite a number of localities in northwestern Mexico, and was thus enabled to obtain a pretty good general idea of the geology of that region; and, in Sonora, to which my attention was especially devoted, I succeeded in finding fossils in sufficient quantity to allow of the determination of the age of the principal formations of the northern Sierra Madre. By tracing the connection of these rocks with those of Central Mexico, additional light will be thrown on those districts of which, at present, but little is definitely known. "The igneous rocks, which occur more abundantly on the Pacific slope, are granites, either fine or very coarse-grained; porphyries, more or less feldspathic; and greenstones, all of which are cut by numerous dikes of extremely varied character. The granites, however, are very poor in veins of the precious metals, while the porphyrics are highly metalliferous. In Sinaloa (Candelero) and Durango (San Dimas) we see that the granites underlie the metallifercus porphyries, and that the greenstones, in Sonora, (near Hermosillo and in the vicinity of La Haciendita,) penetrate through them. The oldest sedimentary rocks which I have observed belong to the carboniferous series; this is represented in the eastern part of Sonora by heavy masses of limestone, forming very high and rugged ridges, running a little west of north. The upturned strata are seen in many places to rest on granite. Argentiferous veins occur throughout this formation. "The next group of sedimentary rocks in order is the triassic; this forms isolated mountain groups in Sonora, and offers an interesting field for investigation. Instead of limestones, it is made up of heavy beds of quartzites and conglomerates, with coal-bearing clay shales; all of these are disturbed and elevated, and rest on greenstones, feldspathic porphyries, or granite. Wherever metamorphosed, the triassic rocks are auriferous and contain veins of silver ores. The metamorphic slates and limestones of the Altar and Magdalena districts, which include the richest gold placers of Sonora, may possibly be of triassic age; but the fossils collected are too imperfect to admit of this being determined. There are some reasons for believing those rocks to be rather of jurassic than of triassic age, as they differ in lithological characters from both the triassic and carboniferous of northern Mexico, * Proceedings Cal. Acad. Nat. Sciences, vol. III, pp. 245-258. † See Emory, in Mexican Boundary Report, vol. 1, p. 41. resembling rather the jurassic gold-bearing slates of the Sierra Nevada, in California; besides, they lie outside and to the west of the Sierra Madre. It may also be noticed that the gold which they furnish does not resemble that obtained from the triassic strata. "The cretaceous period is also represented at the foot of the Sierra Madre, at Arivechi, in Sonora. The strata belonging to this series are chiefly argillaceous shales, and they rest upon porphyries and carboniferous limestone. They have been disturbed and elevated since their deposition. The fossils, which they contain in great number and in a fine state of preservation, will be noticed further on. "All the above-mentioned formations were already in existence before the first eruption of the volcanic rocks took place. These latter are found scattered along the whole Pacific coast, and extend from the Gulf of California up to the very summit of the Sierra. It is very interesting to see the volcanic formations spread over so extensive a region, especially as there are no active volcanoes known in northern Mexico, and not even any indications of ancient craters or vents. MINES.-The richest and widest veins are those northeast of Mazatlan, near San Dimas, Guarisamey, &c., in Durango. These veins cut all the rocks older than the cretaceous, whether igneous or sedimentary. The mines of Sinaloa are richer than those of Sonora. In the former state the ore-bearing portion of the veins is from a few feet to several yards in width; in the latter, generally from one to two feet. In Durango and Sinaloa, gold, native silver, and sulphuret of silver occur, associated with galena, yellow blende, and iron pyrites. In Sonora the principal ores are argentiferous gray copper, with galena, black blende, copper pyrites, arsenical pyrites, carbonate of lead, ruby silver, arsenical silver, and gold. Each mining district is characterized by a peculiar system of veins; in all as many as 20 different systems have been observed. The most abundant vein stones are quartz, either chalcedonic, crystalline, or massive; brown spar; heavy spar; oxide of iron. The veins occurring in the metamorphic triassic rocks are usually parallel with the stratification, so that they lie nearly horizontal where the formation has been but little disturbed. As to the yield of the silver ores, it varies extremely, and it would be necessary to enter into a full description of all the different districts to give an idea of it. It may be noticed, however, that the arsenical pyrites, which is auriferous in the Sierra Nevada, becomes argentiferous in the Sierra Madre. The veins vary in their direction from a little east to a little west of north; the richest ores near San Dimas run northeast and southwest. There are but few rich mines in Sonora, a state of which the mineral wealth has been much exaggerated. There are, however, some deposits of variegated copper, and veins of magnetic and specular iron. The annexed tabular statement will give the principal facts obtained with regard to the mines examined in northern Mexico: |