The Highlands of the Hudson — Magnetic Iron Ores. 23 



fault whose plane dips east, and whose course is nearly due north, or 

 oblique to the strike of the ore.* 



The polished slickensides surfaces, which traverse the ore, indicate 

 fractures and movements to an unusual extent. The presence of 

 numerous pseudomorph minerals also points indirectly to a vast 

 amount of fracturing.! The ore is fine-crystalline, and consists of 

 magnetite, mixed with some chondrotite and serpentine. It is a 

 Bessemer ore. As shipped it averages 50 per cent of metallic iron.| 

 Owing to the shaky condition of the roof, and the difficulty of sup- 

 porting it by pillars of ore and of masonry, the gigantic feat of 

 removing the whole of the superincumbent rock from an area of about 

 400 by 300 feet, to a depth of 300 feet, was begun in 1887. In this 

 way the ore in the pillars can be won, and the mine worked as an 

 open pit to a depth of 600 or 650 feet. 



As this work is done under a special contract, the company is not 

 mining any ore.§ The lean ore, which occurs interstratified with the 

 rich, is being stocked in huge dumps at the side of the great pit for 

 future concentration. The rich, furnace ore is used at the furnaces 

 of the Lackawanna Iron and Coal Company, at Scranton, Penn., and 

 Franklin Furnace, N. J. 



A mill for the concentration of the lean ores, equipped with Blake 

 crushers, Michigan stamps and Conkling jigs, has been erected north 

 of the mine, at the side of the railroad, but is not fairly in operation. 

 The total production of this mine, to the end of 1888, is 620.162 

 tons. It was opened in 1864. Since 1879, the "Tilly Foster Iron 

 Mine Co." have been owners of the property. 



* A full description of the geology of the Tilly Foster Mine, is given by Ferdinand 

 S. Ruttmann, of New York city, in the Trans. Am. Inst. Min. Engineers, Vol. XV, 

 pp. 79-90. See also paper by A. F. Wendt, in Vol. XIII, pp. 478-34, same series. 

 t "On Serpentine, Pseudomorphs and other kinds, from the Tilly Foster Iron Mine 

 Putnam Co., N. Y., by James D. Dana." Am. Jour. Science (3), Vol. VIII, pp. 371- 

 381, and 447-459. 



% An analysis shows the ore to contain : 



Oxides of iron 67.42 per cent. 



Oxide of Manganese .54 



Alumina 3.85 



Lime 1.44 



Magnesia 13.30 



Sulphur 0.11 



Phosphoric acid 0.128 



Silica 13.23 



100.018 

 Communicated by S. P. Tompkins, Superintendent. 

 "§ For an account of this work of uncovering, see paper by F. H. McDowell, of New 

 York city, to appear in Vol. XVII., Trans. Am. Inst. Min. Eng. 



