Stratified volcanic deposits cover a broad area of the surface between San Ignacio and San Dimas (Sinaloa and Durango); they dip to the west. On the other side of Durango they dip in the opposite direction. The serrated edges of the strata may be seen from a great distance, and are extremely picturesque, towering up like old ruins, their peculiar forms being due to erosion. They are well seen in the Cerro de los Frayles, near Guarisamey, in Durango; visible from Mazatlan. These belong to the second series of volcanic rocks. In Sonora there are three different series of volcanic deposits which form serrated, picturesque, parallel ridges, running north from Guaymas as far as La Magdalena, or over eighty leagues in a straight line. The three main ridges, enumerated from west to east, are, 1, Las Tetas de Cabra; 2, Guaymas de Zaragosa; 3, Range north of the mouth of the Yaqui River. The description of the various volcanic deposits of Northern Mexico may be reserved for a separate memoir, as the number of them is very great. MINES. The richest and widest veins are those northeast of Mazatlan, near San Dimas, Guarisamey, etc., 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 twenty 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