Note 4 — MINERALS. (continued 3)

They are also found in a kind of natural clefts which cross the regular mineral beds or strata in different directions (Pl. I, Fig. 1, a, Pl. I, Fig. 4, b). When these 3contain metallic ores, they are styled veins; but when they contain only stony or earthy matters, the miners call them dykes. They vary much both in magnitude and length. Six thousand feet are considered an unusual length for veins, though, in some instances, veins have been traced upwards of four miles. Few veins extend more than 1200 feet below the surface of the mountains in which they are situated. They are usually much inclined; but they sometimes descend in a direction parallel with the beds of rock in which they occur.