« ForrigeFortsett »
is increased, and there is attached to the lower end of the suspension bars a suitable frame, which, in combination with the "carrier," is furnished with joints, enabling all necessary angles and curves to be passed. Figs. 5 and 6 show the double carrier for conveying a self-dumping bucket or car holding 500 pounds of ore. By increasing the number of Fig. 5.
carriers, and thus distributing the load along the rope, the load or weight to be conveyed can be also increased.
The rope being set in motion, carries with it the various loads of ore or whatever material is transported; passing without impediment all the bearing and guide-pulleys, as well as the end grip-pulleys. On account of the arrangement of the bearing and guide pulleys a and b, Fig. 3, the rope cannot jump out from the groove of the pulleys under any circumstances, while they permit the rope and its load to pass over any mountain or through any valley.
The curves are passed in two ways. For a very acute angle two horizontal grooved pulleys are employed, the rope of the interior angle passing around in manner shown in plan, Fig. 7; and for ordinary curves a series of pulleys are so placed that the rope always leads fair on to the next pulley, being deflected in passing off at an angle not to exceed 110, until the curve is completed. This manner is shown in Fig. 8. Fig. 9 shows another mode of conveying the ore. The car being on an
inclined track, is taken up by the carrier, which has attached to the lower end an inclined bar fitted with notches.
The speed of the rope is usually 200 feet per minute. If the ore-sacks contain 150 pounds, and are suspended every 50 feet, 36,000 pounds are delivered per hour, at a cost, including interest, wear and tear, &c., estimated by the patentee at from 20 to 40 cents per ton per mile.
ELECTRICITY AND ROCKS.
This chapter was read by me as a paper before the American Insti tute of Mining Engineers, at their Troy meeting, in November, 1871. * There is much vague theorizing about the connection between elec trical currents or discharges and the formation of mineral deposits, and those who substitute the word "magnetism" for "electricity" mean probably the same thing. There is no need of being exact when one is explaining things on a grand scale, and without reference to the details, that is to say, the facts!
In a brief treatise on mineral-deposits, contained in my report of 1870 on mines and mining, I have intimated my view of the limits to which electrical theories of vein phenomena should be confined, namely, those of chemical reactions, either taking place in vapors or solutions of mineral substances, and resulting in precipitation, or occurring in the permeable contents of mineral-deposits already once mechanically or chemically precipitated, and resulting in varied metamorphosis. In the latter case, as well as in the former, the process, strictly speaking, involves the presence of vapors or liquids, since this is a condition of all chemical reactions. The effects produced, aside from such as I have described, by the mere transmission of magnetic or electrical currents through solid rocks, I believe to be trivial and rare. Mr. Darwin, in his "Voyage of the Beagle," describes the vitrified siliceous tubes of La Plata, caused by lightning entering loose sand. In the second volume of the "Geological Transactions," referred to by the same author, there is an account of the similar formations, called fulgurites, occurring at Drigg, in Cornwall; and another case is described by Ribbentrop, in Germany. I quote a part of Darwin's description:
"Four sets entered the sand perpendicularly; by working with my hands I traced one of them two feet deep; and some fragments, which evidently had belonged to the same tube, when added to the other part, measured five feet three inches. The diameter of the whole tube was nearly equal, and therefore we must suppose that originally it extended to a much greater depth. These dimensions are, however, small, compared to those of the tubes from Drigg, one of which was traced to a depth of not less than thirty feet.
"The internal surface is completely vitrified, glossy, and smooth. A small fragment exhibited under the microscope appeared, from the number of minute entangled air, or perhaps steam-bubbles, like an assay fused before the blow-pipe. The sand is entirely, or in greater part, siliceous; but some points are of a black color, and from their glossy surface possess a metallic luster. The thickness of the wall of the tube varies from a thirtieth to a twentieth of an inch, and occasionally even equals a tenth. On the outside the grains of sand are rounded, and have a slightly glazed appearance. I could not distinguish any signs of crystallization. In a similar manner to that described in the Geological Transactions, the tubes are generally compressed, and have deep longitudinal furrows, so as closely to resemble a shriveled vegeta ble stalk, or the bark of the elm or cork tree. Their circumference is about two inches, but in some fragments, which are cylindrical and
without any furrows, it is as much as four inches. The compression from the surrounding loose sand, acting while the tube was still softened, has evidently caused the creases or furrows. Judging from the uncompressed fragments, the measure or bore of the lightning (if such a term may be used) must have been about one inch and a quarter. At Paris, M. Hachet and M. Beudant succeeded in making tubes, in most respects similar to these fulgurites, by passing very strong shocks of galvanism through finely-powdered glass; when salt was added, so as to increase its fusibility, the tubes were larger in every dimension. They failed both with powdered feldspar and quartz. One tube, formed with powdered glass, was very nearly an inch long, namely, 0.982, and had an internal diameter of 0.919 of an inch. When we hear that the strongest battery in Paris was used, and that its power on a substance of such easy fusibility as glass was to form tubes so diminutive, we must feel greatly astonished at the force of a shock of lightning, which, striking the sand in several places, has formed cylinders, in one instance at least, thirty feet long, and having an internal bore, when not compressed, of full an inch and a half; and this in a material so extraordinarily refractory as quartz!"
It is unnecessary to dwell upon the power of electricity thus manifested. It is manifested to us in several instances where houses are struck by lightning, and metallic objects are instantly melted by the surcharging current. What I wish to point out is the comparative rarity of such electrical effects in nature, and particularly in ore-deposits. We do not find in these, as a general rule, any traces of vitrifying fusion, and we may fairly conclude that they are not particularly liable to this form of electrical action. It has, however, occurred to me that some puzzling cases in mineralogy might be due to this cause. Every mineralogist now and then encounters specimens sincerely alleged to be native, i. e., in a natural state, but which he recognizes as the products of more or less perfect fusion. In most instances, no doubt, the fusion has been artificial, and the specimens are really forge or furnace products. Sometimes, however, they may be really native, and vitrified by lightning. Mr. Daubré, in a paper on meteorites in the Annales des Mines for 1868, remarks that lightning produces on the rocks of the earth a varnish which is not without analogy to that of meteorites. It occasions, namely, on certain rocks, particularly toward the summit of mountains, the formation of little drops, or of a glaze, to which De Saussure first called attention. It was on account of this resemblance that the savants to whom certain meteorites were submitted, which fell at Lucè in 1768, expressed their opinion that they were merely terrestrial stones vitrified by lightning.
But the rarity and comparatively insignificant extent of such phenomena, and the fact that nothing of the kind is observed as normal to mineral-deposits, even at their outcrops, warrants me in saying that electrical discharges of this character cannot be considered as active agents in the formation, filling, or metamorphosis of veins.
I pass to consider another class of electrical phenomena, namely, those connected with the electric resonance or boudonnement of mountains. Mr. George S. Dwight, of Montclair, New Jersey, has communicated to me a recent case of this kind, personally observed by him on Gray's Peak, in Colorado, the highest summit of the Rocky Mountains. He ascended this peak with a party about the 10th of June last, reaching the top at 2 p. m. Clouds had been gathering for an hour or two, and storms were in progress on the adjoining ranges, principally to the north and east, with heavy, rumbling thunder at brief intervals. "A