Annual report of the United States Geological Survey to the Secretary of the Interior . dal. In mining it givesoff a fine, chocolate-brown dust, most penetrating to skin and near the outcrop of the vein to be influenced by atmos-pheric agencies, it loses its brilliant luster for a dead-black surface,but a fresh fracture, no matter in how small a particle, shows its17 geol, pt i 59 930 THE UINTAITE DEPOSITS OF UTAH. brilliancy still present, indicating a change to an inconsiderable depthonly. Under atmospheric influences, also, uintaite shows a tine colum-nar structure at rig
Annual report of the United States Geological Survey to the Secretary of the Interior . dal. In mining it givesoff a fine, chocolate-brown dust, most penetrating to skin and near the outcrop of the vein to be influenced by atmos-pheric agencies, it loses its brilliant luster for a dead-black surface,but a fresh fracture, no matter in how small a particle, shows its17 geol, pt i 59 930 THE UINTAITE DEPOSITS OF UTAH. brilliancy still present, indicating a change to an inconsiderable depthonly. Under atmospheric influences, also, uintaite shows a tine colum-nar structure at right angles to the walls of the vein and to a distanceof about G inches from them. This structure has been recognized byWurtz, Lesley, and others in grahamite, and by Lesley is called pen-cillate. In addition to the columnar, there maybe developed a cuboidalstructure, in some instances by a further transverse separation of thepencillate rays; in others independent of these. In the upper 10 or 15feet of a vein the latter structure not infrequently prevails through a R I E Uinta Mer REE. A-A,vein of uintaite Scale —?—Roadso I Fig. 26.—Sketch of region about Fort Duchesne, Utah. large proportion of the uintaite, shading laterally into the two pencil-late zones at the sides. It would seem quite probable that this struc-ture, pencillate and cuboidal, is inherent in the material, havingoriginated perhaps immediately after its injection into the fissure fromcooling or from pressure. The walls of the uintaite veins are usually impregnated with the min-eral to depths of from G inches to 2 feet, though the shales, on accountof their close texture, do not permit this to such a degree as the sand-stones. The line between the impregnated and nonimpregnated por-tions of the wall rock is usually somewhat indefinite, but instances arenot wanting of the sharpest demarcation. ELDRIDGE.] THE VEINS. 931 LOCALITIES (>F THE VEINS.
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