METALLIFEROUS DEPOSITES. 335 



CIUP.XXVI 



X. INTENDANCY OF PUEBLA. 



Several Mines. 



XI. INTENDANCY OF VERA CRUZ. 



Three Mines. 



XII, OLD CALIFORNIA. 



One Mine. 



In the present state of the country tlie veins are the Productive 

 most productive, and tlie minerals disposed in beds or ''""^ 

 masses are very rare. The former are chiefly in primi- 

 tive or transition rocks, rarely in secondary deposites 

 In the Old Continent granite, gneiss, and mica-slate, 

 form the central ridges of the mountain-chains ; but in 

 the Cordilleras of America these rocks seldom appear 

 externally, being covered by masses of porphyry, green- 

 stone, amygdaloid, basalt, and other trap-formations. 

 The coast of Acapulco is composed of granite ; and as 

 we ascend towards the table-land of Mexico, we see it 

 pierce the porphyry for the last time between Zumpango 

 and Sopilote. Farther to the east, in the province of 

 Oaxaca, granite and gneiss are visible in the high plains 

 which are of great extent, traversed by veins of gold. 



Tin has not yet been observed in the granites of 

 Mexico. In the mines of Comanja syenite contains a 

 seam of silver ; while the vein of Guanaxuato, the 

 richest in America, crosses a primitive clay-slate passing 

 into talc-slate. The porphyries of Mexico are for the 

 most part eminently rich in gold and silver. They are Gold, silver 

 all characterized by tlie presence of hornblende and the ''"' 

 absence of quartz. Common felspar is of rare occur- 

 rence, but the glassy variety is frequently observed in 

 them. The rich gold-mine of Viilalpando, near Gua- 

 naxuato, traverses a porphyry, of which the basis is 

 allied to clinkstone, and in which hornblende is ex- 

 tremely rare. The veins of Zimapan intersect porphy- 

 ries, having a greenstone basis, and contain a great 

 variety of interesting minerals, such as filirous zeolite, 

 etilbite, grammatite, pycnite, native sulphur, fluor, 



