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in which samphibole is extremely rare. Several of these parts of New Spain bear a great analogy to the problematical rocks of Hungary, designated by M. Born by the very vague denomination of saxum metalliferum. The yeins of Zimapan which are the most instructive in respect to the theory of the stratification of minerals are intersected by porphyries of a greenstone base which appear to belong to trap rocks of new formation. These veins of Zimapan offer to oryctognostic collections a great variety of interesting minerals such as the fibrous zeolith, the stilbite, the grammalite, the pycnite, native sulphur, spar fluor, baryte suberiform asbestos, green grenats, carbonate and chromate of lead, orpiment, chrysoprase, and a new species of opal of the rarest beauty, which I made known in Europe, and which M. M. Karsten and Klaproth have described under the name of (feuer-opal.) . . · Among the transition rocks which contain silver minerals, we may mention the transitionlime-stone (übergangs-kalkstein) of the Real del Cardonal, of Xacala and of Lomo del Toro, to the north of Zimapan. In the last of these places what is worked is not veins but masses of galena, of which some nests have yielded in a short space of time according to the observation of M. Sonneschmidt, more than 124,000 quintals of lead. The grauwakke alternating

with the grauvakken slate is equally rich in metals in Mexico as in several parts of Germany. In this rock the formation of which immediately preceded that of the secondary rocks, several of the veins of Zacatecas appear to be found. :.

In proportion as the north of Mexico shall be examined by intelligent geologists, it will be perceived that the metallick wealth of Mexico' does not exclusively belong to primitive earths and mountains of transition, but extend also to those of secondary formation. I know not whether the lead which is procured in the eastern parts of the intendancy of San Luis Potosi" is found in veins or beds, but it appears certain, that the veins of silver of the real de Catorce, as well as those of the Doctor and Xaschi near Zimapan, traverse the alpine" lime-stone (alpenkalkstein); and this rock 'reposes on a poudingue with silicious cement which may be considered as the most antient of secondary formations. The' alpine lime-stone and the jura lime-stone (jurakalkstein) contain the celebrated silver 'mines of Tasco and Teuilotepec in the intendancy of Mexico; and it is in these calcareous rocks that the numerous veins which in this country have been very early wrought, display the greåtest wealth, They are more sterile in the strata of primitive slate (ur-thon-schiefer) which 'as is seen in the

Cerro de San Ignacio, serves for base to the secondary formations.

The result of this general view of the metalliferous depositories (erzführende lagerstätte) is that the cordilleras of Mexico contain veins in a great variety of rocks, and that those rocks which at present furnish almost the whole silver annually exported from Vera Cruz, are the primitive slate, the grauwakke, and the alpine lime-stone, intersected by the principal. veins of Guanaxuato, Zacatecas and Catorce. Thus it is in a primitive slate (ur-thon schiefer) on which a clayey porphyry containing grenats : reposes, that the wealth of Potosi in the kingdom of Buenos-Ayres is contained. On the other hand, in Peru the mines of Gualgayoc or Chota and that of Yauricocha or Pasco which together yield annually double the quantity of all the German minés, are found in an alpine limestone. The more we study the geological constitution of the globe on a large scale the more we perceive that there is scarcely a rock which has not in certain countries been found eminently metalliferous. The wealth of the veins is for the most part totally independent of the nature of the beds which they intersect.

We observe in the most celebrated mines of Europe, that the mining operations are either directed to a multitude of small veins as in the primitive mountains of Saxony, or to a very

small number of depositories of minerals of an
extraordinary power, as at Clausthal, the Harz,
and near Schemnitz in Hungary. The cor-
dilleras of Mexico offer frequent examples of
these two methods of operation; but the dis-
tricts of mines of the most constant and con- :
siderable wealth, Guanaxuato, Zacatecas and
the Real del Monte, contain only one prin-
cipal vein each (veta madre). The vein called.
halsbrükner spath of which the extent is two
metres* and which has been traced for a length
of 6200 metrest is spoken of as a remarkable:
phenomenon at Freiberg. The veta madre of
Guanaxuato, from which there has been ex-
tracted during the course of the last ten years
more than six millions of marcs of silvert, is of
the extent of from 40 to 45 metress, and it is.
wrought from Santa Isabella and San Bruno to
Buena-Vista, a length of more than 12700
metres".

In the Old Continent, the veins of Freiberg: and Clausthal which intersect mountains of gneiss and graunakke are visible in table lands of which the elevation above the level of the sea is only from 350 to 570 metres ; and this

* 6] feet. Trans.
+ 20,341 feet. Trans.
$ 9,937,899*IB. troš. Trans.

From 131 to 147 feet. Trans
| 41,665 feet. Trans.

From 1148 to 1869 feet. Trans.

more

.. elevation may be regarded as the mean height of the most abundant mines in Germany. But in the New Continent the metallic wealth is deposited by nature on the very ridge of the cordilleras, and sometimes in situations within a very small distance from the limit of perpetual snow. The most celebrated mines in Mexico are at absolute heights of from 1800 to 3000 metres*. In the Andes the districts of mines of Potosi, Oruro, Paz, Pasco and Gualgayoc are in regions of which the elevation surpasses that of the highest summits of the Pyrenees. Near the small town of Micuipampa, the great square of which according to my measurement is 3618 metrest above the level of the sea, a mass of silver mineral known by the name of Cerro de Gualgayoc abounds with immense wealth at an absolute height of 4100 metrest. .

We have mentioned in another places the advantage which in working the Mexican mines, is derived from the most important veins being in a middle region where the climate is not unfavourable to agriculture and vegetation. The large town of Guanaxuato is placed in a ravin, the bottom of which is somewhat

* From 5904 to 9842 feet. Trans..
+ 11,868 feet. Trans.
$ 13,451 feet. Trans.
$ See vol i. p. 71, and vol, ii. p. 407,

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