Page:EB1911 - Volume 20.djvu/274

 16, 24, 30 and 50 meshes per linear inch. The several products are treated each on its own magnetic machine, yielding the franklinite for the zinc oxide grates, and followed by spiegel furnace; the residue, which is jigged, yields the zinc silicate and oxide for the spelter furnaces, and waste carrying the calcite, quartz and mica.

Asbestos, when of good quality, is in compact masses, which by suitable bruising and beating are resolved into fine flexible fibres. The Canadian asbestos is associated with serpentine, and is crushed by breakers to in., screened on in., in. screens to reject fines. The values are removed by hand-picking and are crushed by rolls carefully set so as not to break the fibre; this product is then sized by screens and the various sizes are sent to the Cyclone pulverizer, which by beating liberates the individual fibres. It then goes to a screen with eleven holes to the linear inch, and yields a granular undersize and oversize, and a fibrous oversize which is drawn off by a suction fan to a settling-chamber with air outlets covered by fine screen cloth. This fibrous product is the clean mineral for the market. A special treatment separates the fibres of different lengths.

The usual method of dressing corundum and emery, after the preliminary breaking, is to treat the material in an edge-stone mill fitted with light wooden rollers. The action is that of grinding one particle against another, whereby the talc, chlorite, mica, &c., are worn off from the harder mineral. A constant current of water carries off the light impurities. This is called the “muller” process. At Corundum Hill, North Carolina, the first step in removing the impurities from “sand” corundum is to subject it to the scouring action of a stream of water while it is being sluiced from the mine to the mill, the action being increased by several vertical drops of 5 to 10 ft. in the sluice. After reaching the mill all that will not pass through a 14-mesh screen is crushed by rolls, and the undersize of the screen is treated in a washing trough; this removes part of the light waste, and the “mullers” mentioned above complete the cleaning.

Graphite occurs in schist, but being of less specific gravity than the other minerals which enter into the composition of the schist, it settles later than they do. It also breaks into thin scales, which reduces its settling rate still further. The ore is broken by breakers, and by Chile edge-stone mills or by gravity stamps, to a size varying with the character of the minerals from perhaps to in. diameter. The pulp is then conveyed through a series of settling tanks of which the later are larger than the earlier. The quartz and other waste minerals settle in the earlier tanks, while the graphite settles later: the latest tank gives the best graphite. In the Dixon Company’s works in New York some forms of concentrators are believed to have replaced the slower settling tanks.

The phosphates of Florida are of four kinds: hard rock, soft rock, land pebble and river pebble. The hard rock is crushed by toothed rolls, and cleaned in log washers. The washed product is screened; the sizes finer than in. are thrown away because too poor; the other sizes are dried and sold, some waste having been picked out of the coarsest. The soft rock is simply dried, ground and sold. Land pebble is treated by log washers, any clay balls remaining being removed by a screen, and the phosphate dried and sold. In special cases land pebble is treated by hydraulicking, followed by a log washer, and this again by a powerful jet washer, to remove the last of the clay. River pebble is taken from the river by centrifugal pumps, and screened on two screens with 1-in. and -in. holes respectively; the oversize of the first sieve and the undersize of the second sieve are thrown away because of too low grade.

OREGON, a North-Western state of the American Union, on the Pacific slope, lying between 42° and 46° 18′ N. lat. and 116° 33′ and 124° 32′ W. long. It is bounded N. by the state of Washington, from which it is separated in part by the Columbia river, the 46th parallel forming the rest of the boundary; E., by Idaho, from which it is separated in part by the Snake river; S., by Nevada and California, and W., by the Pacific Ocean. It has an extreme length, E. and W., of 375 m., an extreme width, N. and S., of 290 m., and a total area of 96,699 sq. m., of which 1092 sq. m. are water-surface.

Topography.—The coast of the state extends in a general N. and S. direction for about 300 m., and consists of long stretches of sandy beach broken occasionally by lateral spurs of the Coast Range, which project boldly into the sea and form high rocky headlands. With the exception of the mouth of the Columbia river, the bays and inlets by which the shore is indented are small and of very little importance. Parallel with the coast and with its main axis about 20 m. inland is an irregular chain of hills known as the Coast Range. It does not attain a great height, but has numerous lateral spurs, especially toward the W. Euchre Peak (Lincoln county), probably the highest point in the range in Oregon, rises 3962 ft. above the sea. In southern Oregon the general elevation of this range is greater than in the N., but the individual peaks are less prominent, and the range in some respects resembles a plateau. Its western slope is generally longer and more gentle than the eastern. A number of small streams, among them the Nehalem, Coquille and Umpqua rivers, cut their way through the Coast Range to reach the ocean. For the greater portion of its length in Oregon, in the northern half of the state, the Coast Range is bordered on the E. by the Willamette Valley, a region about 200 m. long and about 30 m. wide, and the most thickly populated portion of the state; here, therefore, the range is easily defined, but in the S., near the Rogue river, it merges apparently with the Cascade and the Sierra Nevada Mountains, lying partly in Oregon and partly in California, and extending from the northern extremity of the Sierra Nevada to the sea. The Klamath Mountains separate topographically southern Oregon from northern California. A number of ridges and peaks bearing special names, such as the Rogue river, Umpqua and Siskiyou Mountains, belong to this group. The Cascade Mountains, the most important range in Oregon, extend parallel with the coast and lie about 100 m. inland. The peaks of this system are much higher than those of the Coast Range, varying from 5000 to 11,000 ft., and the highest of them are cones of extinct volcanoes. Mount Hood (11,225 ft.), which is the highest point in the state, Mount Jefferson (10,200 ft.), the Three Sister Peaks, Mount Adams, Bachelor Mountain, and Diamond Peak (8807 ft.) all have one or more glaciers on their sides. The Calapooya Mountains, forming the water-parting between the Willamette and the Umpqua rivers, are a lateral spur of the Cascades, and extend westward as far as the Coast Range. The Cascade Mountains divide the state topographically into two sharply contrasted parts. West of this range the country exhibits a great variety of surface structure, and is humid and densely wooded; east of the range it consists of a broken tableland, arid or semiarid, with a general elevation of 5000 ft. This eastern tableland, though really very rugged and mountainous, seems to have few striking topographic features when compared with the more broken area to the W. In the north-eastern part of this eastern plateau lie the Blue Mountains, which have an average elevation of about 6000 ft. and decline gradually toward the N. A south-western spur, about 100 m. in length, and the principal ridge together enclose on several sides a wide valley drained by the tributaries of the John Day river. South of these mountains lies the northern limit of the Great Basin region. In Oregon this area extends from the Nevada boundary northward for about 160 m., to the head of the Silvies river, and embraces an area of about 16,000 sq. m. None of its streams reaches the sea, but all lose their waters by seepage or evaporation. On the E., N., and N.W. the Great Basin is bounded by the drainage systems of the tributaries of the Columbia river, and on the S.W. by the drainage system of the Klamath river. Its boundaries, however, cannot be definitely fixed, as they change with the periods of humidity and drought. Goose Lake, for example, lies in the Great Basin at some seasons; but at other times it overflows and becomes a part of the drainage system of the Sacramento river. Many of the mountains within the Basin region consist of great faulted crust blocks, with a general N. and S. trend. One face of these mountains is usually in the form of a steep palisade, while the other has a very gradual slope. Between these ridges lie almost level valleys, whose floors consist partly of lava flows, partly of volcanic fragmental material, and partly of detritus from the bordering mountains. During the wet season the valleys often contain ephemeral lakes, whose waters on evaporating leave a playa, or mud flat, often covered with an alkaline encrustation of snowy whiteness. Some large permanent lakes occupy the troughs between faulted blocks in southern Oregon. The greatest level, or approximately level, area in the Great Basin region of Oregon is the so-called Great Sandy Desert, a tract about 150 m. long and from 30 to 50 m. wide, lying in parts of Crook, Lake and Harney counties. Its surface consists of a thick sheet of pumiceous sand and dust, from which arise occasional buttes and mesas. On account of the small amount of precipitation, the fissured condition of the underlying lava sheets, and the porous soil, the Great Sandy Desert has practically no surface streams even in the wet season, and within its limits no potable waters have been found. The most prominent mountain range in the Oregon portion of the Great Basin is the Steens Mountains in the S.E., which attain an altitude of about 9000 ft. above the sea and of 5000 ft. above Alvord Valley, which lies along the eastern base. This range is a large monoclinal block, with a trend almost N.E. and S.W., presenting a steep escarpment toward the E., and sloping very gradually toward the W. It exhibits much evidence of powerful erosion, having deep canyons in its sides, and it bears evidence of previous glaciers. The region adjoining the Great Basin on the E. is usually known as the Snake River Plains, and embraces an area of about 1200 sq. m. in Malheur county. Here the hills are deeply sculptured and the valleys much carved by streams which often flow through deep canyons. Where the streams cut their way through sheets of basaltic lava their banks are steep, almost vertical cliffs, but where they cut through sedimentary rocks the sides have a more gentle slope. When several alternate layers of hard and soft rock are cut through by a stream its banks sometimes have the form of steps. The destruction of the grasses on the hillsides by overgrazing in recent years has increased the flooding by temporary streams, and consequently has tended to deepen and increase the gulleys and channels of the mountains and valleys.

The state as a whole has an average elevation of 3300 ft.; with 20,300 sq. m. below 1000 ft.; 19,200 sq. m. between 1000 and 3000 ft; 33,500 sq. m. between 3000 and 5000 ft.; and 23,030 sq. m. between 5000 and 9000 ft.