MAGNETITE IRON DEPOSITS OF SOUTHEASTERN NEW YORK 67 
between the magnetite grains, and in the rare cases where the ores 
are sufficiently titaniferous to show intergrowths of magnetite and 
ilmenite. (Plate 11, figure 3) 
The presence of corroded, more or less altered remnants of 
various minerals (unreplaced remnants) and of minerals co-related 
in origin to the magnetite, such as apatite, interrupts the continuity 
of the magnetite to such a degree that all polished surfaces of the 
ore appear strongly pitted and irregular as to the distribution of the 
magnetite itself. This is shown in plate 11, figures 1 to 5. These 
photomicrographs were taken in direct reflected light from polished 
plates of the ore. The magnetite appears in white scattered areas, 
pitted and patchy because of the included matters mentioned. The 
irregular, corroded, smooth grayish patches are remnants of unre- 
placed silicate minerals. Figure 3, in the same group, is an etched 
slab of ore from the Canopus mine showing the distribution of 
platelike ilmenite intergrown with the magnetite. 
The chemical composition of the ores accords perfectly with the 
general make-up and habit of the magnetite as shown by the micro- 
scope. 
The writer has been unable to have chemical analyses made; some 
of the analyses that have been made in the past appear in the roth 
Census Report, and a few incomplete analyses may be found in other 
reports. From these data, and from a petrographic study of the 
ores, it appears that there are three general types of ore: (1) a 
high phosphorus, low sulphur, non-Bessemer magnetite; (2) low 
phosphorus, high sulphur ore, and (3) an intermediate type carrying 
moderate quantities of both sulphur and phosphorus, but not of 
Bessemer grade. An additional and rare type was derived from 
the Mahopac and Tilly Foster mines, low in phosphorus, low to 
moderate in sulphur, but carrying silica, lime and magnesia, as lime- 
magnesia silicates (see plate 9, figure 1, plate 14, figures 3 and 4) in 
such proportions and in such quantities as to make the ores “ self- 
fluxing.” The general composition of these four types is as fol- 
lowest. 4 
2 Tenth Census Report (1880); published in 1886. 
