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edifices, both of a public and private character. For bridges, roads, and other works of internal improvement they likewise furnish the most approved materials. By burning, a good quicklime for mortar can almost always be obtained.
METALLIC ORES.
Of the different metallic ores occurring in this formation, the most important are those of silver, lead, and iron.
Silver, associated with sulphur and lead in the form of argentiferous galena, is found along the western base of the Organ Mountains, in New Mexico. The ore is there exposed at the surface in veins, all of which are contiguous to eruptive rocks, and occur, at least as far as my own examinations have extended, in thin bedded, hard, compact, dark blue and black crystalline limestone. The veins are all nearly vertical, and preserve a highly tortuous course, their direction being in some places north and south, and in others inclined towards the east and west. Their thickness, including matrix and all, varies from five to ten feet. The ore is often mixed with a small percentage of iron and titanium, and sometimes contains traces of copper and other metals. When pure it yields from four to six ounces of silver to the hundred pounds. Associated with it as a matrix we have calc and fluor spar. Of these two the former greatly predominates, and is for the most part highly discolored with black and red oxide of iron, while the fluor spar occurs mostly in semi-transparent masses, and is of a beautiful green color.
About fifteen miles east of Dona Ana two of these veins are well exhibited. One is situated near the base of the exposed limestone, which is here strongly upheaved, dipping towards the west at an angle of about 80 degrees, and the other near its summit. The first is about eight feet in thickness, and has at one point been partially worked by means of a shaft sunk to the depth of ten feet. The metalliferous portion occupies fully one third of the entire thickness of the vein, and occurs in such a manner as to be very easily separated from the gangue. This vein, at the point examined by myself, has a W. N.' W. bearing, and is traced, as I am informed, for the distance of several hundred yards on both sides of the shaft. From some cause or other it has not been worked for several years past, although, from the character and thickness of the ore, it would doubtless, if properly managed, prove highly profitable. The second vein is about ten feet in thickness, and is at present worked by Mr. Stephenson, who has sunk a shaft in it to the depth of near thirty feet. The ore occurs in a solid sheet from eighteen inches to two feet in thickness, and is also very easily separated from the gangue. After its extraction it is conveyed upon the backs of mules to the place of smelting, a distance of about sixteen miles, and in spite of the great disadvantages attending its present mode of working, the