Strong arguments against the theory that the leaching of superficial igneous rocks has supplied the materials filling mineral veins, are furnished by the facts observed in the districts where igneous rocks are most prevalent, viz.: (1.) _Such districts are proverbially barren of useful minerals_. (2.) _Where these occur, the same sheet of rock may contain several systems of veins with different ores and gangues._ The great lava plain of Snake River, the Pedrigal country of eastern Oregon, Northern California and Mexico are without valuable ore deposits. The same may be said of the Pancake Range and other mountain chains of igneous rock in Nevada, while the adjacent ranges composed of sedimentary rocks are rich in ore deposits of various kinds. A still stronger case is furnished by the Cascade Mountains, which, north of the California line, are composed almost exclusively of erupted material, and yet in all this belt, so far as now known, not a single valuable mine has been opened. In contrast with this is the condition of things in California, where the Sierra Nevada is composed of metamorphic rocks which have been shown to be the repositories of vast quantities of gold, silver, and copper. Cases belonging to this category may be found at Rosita and Silver Cliff, where the diversity in the ores of the mines already enumerated can hardly be reconciled with the theory of a common origin. At Lake City the prevailing porphyry holds the veins of the Ute and Ulay and the Ocean Wave mines, which are similar, and the Hotchkiss, the Belle, etc., entirely different. We have no evidence that any volcanic eruption has drawn its material from zones or magmas especially rich in metals or their ores, and on the contrary, volcanic districts, like those mentioned, and regions, such as the Sandwich Islands, where the greatest, eruptions have taken place, are poorest in metalliferous deposits.