MAGNETITE IRON DEPOSITS OF SOUTHEASTERN NEW YORK 65 
The fault which cut the ore body of the Tilly Foster mine has 
been described in detail by Wendt*°? and Ruttman‘*®; the fault 
crossed the ore body diagonally, striking nearly north and south, 
and dipping eastward about 72°. According to Ruttman, the part 
of the ore body east of the fault was displaced in a direction 20° 
east of south and at an angle of 45° with the horizon, about 130 
feet. The horizontal movement was about go feet. (See fig. 12; 
after Wendt and Ruttman.) 
The Mahopac ore body was cut off by a fault of such magnitude 
as to cause the ultimate abandonment of the mine. The trend of the 
fault is not definitely known, as there is no evidence on the surface 
to show in what direction the fault may strike and with the exception 
of the plans and vertical sections of the ore body, redrawn from 
reproductions of old maps kindly loaned by the Ramapo Ore Com- 
pany (fig. 13) no exact information could be obtained with regard 
to the trend and magnitude of the fault. The throw is probably not 
less than 150 or 200 feet, toward the east or southeast. 
There is some evidence to indicate that the Brewster belt of 
magnetite has been similarly affected, more particularly the Clover 
Hill mine, which lies at the southern end of the belt; but here like- 
wise there are no faults of any great magnitude. 
It seems evident that in but very few instances have the magnetite 
bodies been seriously affected by deformation resulting from fault- 
ing ; even in the questionable cases such as, for example, the Mahopac 
ore body, it is the belief of the writer that properly directed 
exploratory work would locate the faulted-off portion of the ore, 
since none of the transverse faults has very great throw. It is only 
when both Appalachian and Triassic faulting have affected the ore 
bodies that a very serious situation arises, and these cases are rare. 
Character of the magnetite. The magnetite bodies of south- 
eastern New York are in general massive, hard, crystalline ores 
invariably mixed with mineral remnants, sometimes altered, of the 
rocks they have replaced; or, in the case of those deposits resulting 
from the magmatic replacement of interbedded crystalline limestone, 
the ore is mixed with typical contact minerals, some of which may 
have been produced by magmatic action during the replacement ; 
such as tremolite, chondrodite, garnet, scapolite, coccolite, spinel and 
others of similar origin. Other minerals co-related in origin to the 
109 Wendt, A. F. The Iron Mines of Putnam County, N. Y. Trans. A. I. 
IMG Ty, SOM Ae Waste, 
110 Ruttman, F. S. Notes on the Geology of the Tilly Foster Ore body, 
Putnam County, N. Y. Trans. A. I. M. E., v. XV, p. 79-00. 1886-87. 
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