June 16

1874 Proceedings of the Academy of Natural Sciences of Philadelphia  
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more » ... ntent at http://about.jstor.org/participate--jstor/individuals/early-journal--content. JSTOR is a digital library of academic journals, books, and primary source objects. JSTOR helps people discover, use, and build upon a wide range of content through a powerful research and teaching platform, and preserves this content for future generations. JSTOR is part of ITHAKA, a not--for--profit organization that also includes Ithaka S+R and Portico. For more information about JSTOR, please contact support@jstor.org. PROCEEDINGS OF THE ACADEMY OF phyry mountain in all directions. This mountain covers at its base about seventy acres, more or less, and is furrowed by deep cuts near its summit; some of these to a depth of eighty to one hundred feet. The best and purest ore is that which was found lying on the surface of its slopes, and of this there is still a very large quantity; but the large boulders have been almost all removed, while that which remains is so finely divided and so mixed with the clay and soil that any ordinary method of separation would make it too expensive. Lately, the California hydraulic mining has been applied to win this ore, with great success. Water is pumped through large hoses which are led up the sides of the hills, and the debris is washed down through sluice-boxes and over small falls, which agitate it sufficiently to shake the ore from the dirt and allow it to deposit at the foot of the hill by virtue of its higher specific gravity, in receptacles provided for it. The remaining ore is obtained by blasting, is loaded on a gravity railway and carried to the foot of the mountain, where it is dumped, three or four tons at a time, over a shoot which precipitates it some eight or ten feet, upon the flats of the Iron Mountain Railroad Company, which are awaiting it. The shock as this heavy weight strikes the cars is great enough to cause them sometimes to tilt over on two wheels. How much it increases the wear and tear I was unable to ascertain. This ore contains from 65 to 68 per cent. metallic iron, associated with 0.031 per cent. to 0.11 per cent. phosphorus and 4 to 4.5 per cent. silica, and a trace of sulphur. The quantity exposed is enormous, but was stated by Mr. David Thomas, of Catasauqua, not to equal in quantity the celebrated Cornwall mines of this State. The ore from Pilot Knob is much more sandy than that from Iron Mountain. It occurs in a bed dipping with the general dip of the country rock, and inclosed within the porphyry out of which the knob is formed. The formation of this ore is a most interesting study, and the only plausible theory seems to be that of lateral replacement, a case of metasomatism where the porphyry, having become slaty in structure, and less capable of resisting the solvent, has been replaced along the line of strike, and only in such laminated parts. This ore is banded in appearance, and is almost, if not quite, invariably hematite. JUNE 16. The President, Dr. RIUSCHENBERGER, in the chair.
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