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alteration amount andesite angle aplite bands bedding planes Belt group biotite blocks Boulder batholith brecciated Butte calcite character cleavage composition conglomerate contact metamorphism contact surface crystals deposits depth detail dikes dikes and sheets diopside distance Drinkwater Gulch Drumlummon epidote erosion evidence exposed feet feldspar formation fracture gabbros geologic granite gravels groundmass Helena limestone hill hornblende hornstone igneous rock inches indicating infiltration invasion irregular joint planes laccolithic lava limestone limits Little Prickly Pear localities magma margin Marysville batholith Marysville district mass metamorphic zone metasomatic mica microdiorites microscope mile minerals Mount Belmont noted observed occur original orthoclase outcrop parallel pegmatites phenocrysts places plagioclase pneumatolitic porphyry porphyry dikes portions Prickly Pear Creek probably pyrite pyroxene quartz diorite region relations sedimentary sediments segregations shale side siliceous Silver Creek slopes strata structure Tertiary thickness tremolite U. S. Geol valley vein fissures vertical wall rocks
Seite 180 - The Gabbros and Associated Hornblende Rocks occurring in the Neighborhood of Baltimore, Maryland, by George Huntington Williams.
Seite 105 - In general it may be said that all the veins of the district carry rich ores in bonanzas and ore shoots within the first 200 feet from the surface, but that in depth the ores rapidly decrease in value until the vein is no longer workable. It may also be said that the ore shoots were well defined, and the intervening vein matter barren and unworkable. The pitch of the ore shoots conforms to the usual habit, dipping to the right when looking down the dip of the vein. The ores consist of sulphides and...
Seite 89 - defined as a structure in some rocks, by virtue of which they are already separated into parallel laminae in a state of nature.
Seite 179 - Bullfrog, and other mining districts in southern Nevada, by FL Ransome, with notes on the Manhattan district, by GH Garrey and WH Emmons. 1907.
Seite 104 - Weed," who says: In addition to the pneumatolitic deposite on igneous contacts and those in altered strata near the contacts there are many productive mines working true veins cutting the igneous rock and the contact rocks above them. Such vein fissures are caused both by the contraction due to the crystallization and cooling of the igneous rock and by the shrinkage of the metamorphic zone above the igneous rock. Examples of this type have already been mentioned. As shown by Pirsson...
Seite 180 - Price 10 cents. 65. Stratigraphy of the Bituminous Coal Field of Pennsylvania, Ohio, and West Virginia, by Israel C. White. 1891. 8". 212pp. 11 pi. Price 20 cents. 66. On a Group of Volcanic Rocks from the Tewan Mountains, New Mexico, and on the occurrence of Primary Quartz in certain Basalts, by Joseph Paxson Iddings.
Seite 179 - Veatch. 1907. 178 pp., 26 pis. B 308. A geologic reconnaissance in southwestern Nevada and eastern California, by SH Ball. 1907. 218 pp., 3 pis. B 309. The Santa Clara Valley, Puente Hills, and Los Angeles oil districts, southern California, by GH Eldridge and Ralph Arnold. 1907. 266 pp., 41 pis.
Seite 169 - ... probable that at no great depth the granite underlies the greater part of the district. If the granite merely broke through and involved the original rocks of the area it now occupies, their entire absence from it as inclusions is remarkable; if they had been carried away by fresh accessions from below they should be found as inclusions in certain localities preserved from erosion. On the supposition that they have sunk as fast as freed, the absence of inclusions may be readily explained. If,...
Seite 31 - The Helena limestone formation is composed of more or less impure bluish-gray and gray limestone, in thick layers, which weathers to a buff and in many places to a light gray color. Irregular bands of broken oolitic and concretionary limestone occur at various horizons. Bands of dark and gray silicious shale and greenish and purplish argillaceous shale are interbedded in the limestones. These bands are from half an inch to several feet in thickness. There are also beds of thinner bedded limestones,...
Seite 105 - This vein, which is the largest and the most productive in the district, consists in its lower levels of a mass of angular rubbish, derived from the walls of the fissure, and in places cemented by quartz, in other places still retaining its original character. Compared with the Empire and other veins, it is much more extensive, both laterally and vertically, and the values have gone deeper. In general it may be said that all the veins of the district...