Underlying all the rocks in Durango and Sinaloa, and probably posterior to the Carboniferous limestones, which they have in places extensively metamorphosed, are masses of granite. These may be seen in many places between the coast and San Dimas, either occupying the bottoms of the valleys, or forming independent hills. There are two well-marked varieties: Of these the first are syenites, more or less fine-grained, and consisting of a mixture of feldspar, variously colored, quartz, black or green hornblende, and black or brown mica, the latter usually in hexagonal plates. Localities of this variety are: Haval, Las Higueras, San Ignacio, Santa Apolonia, Candelero, La Noria, Zaragoza, etc., in Sinaloa; San Marcial and Tecoripa valleys, Hermosillo, in Sonora. The other variety is either very coarse-grained, consisting of white feldspar, gray quartz, and plates of silvery mica, or else finer grained, and chiefly made up of feldspar; these occur, forming mountains and ridges in Sonora, in the Sierra del Amolé, near La Magdalena, Sierra del Espinaso Prieto, near Hermosillo, and the Sierra de Mazatan, south of Ures. The fine-grained granites contain argentiferous veins at Zaragoza, in Sinaloa, and east of Topisco, in Sonora. These are traversed by numerous intersecting dykes of diorite, feldspar, and quartziferous and feldspathic porphyries, especially well seen near Hermosillo, and the Cajon de los Carrisos, east of San Antonio de la Huerta. There are no metalliferous veins where the granite is thus intersected by dykes. METALLIFEROUS PORPHYRIES. These may be divided into two groups. The first consists of a rock occurring in large irregular masses or beds, and having a dark colored argillaceous base, through which are disseminated small crystals of whitish feldspar. This variety, which is probably older than the granites, includes some of the richest mines of the Sierra Madre; as those of Candelaria, Bolaños, Cinco Señores, etc., near San Dimas, in Durango; and which have yielded over $20,000,000. There are also rich veins in this kind of rock at Candelero, fifty-two leagues northeast of Mazatlan, in Sinaloa. All these veins run northeast and southwest, and are cut at right angles by dykes. The second variety of porphyry is a gray feldspathic rock, apparently made up of labradorite and magnetic iron ore; this overlies the greenstones, and is covered by the Triassic beds at Los Bronces and San Javier, where there are three systems of argentiferous veins. The Nahuila mine, one of the best in Sonora, is in this rock. METAMORPHIC ROCKS.