16 : NEW YORK STATE MUSEUM 
apparent “bedding,” but which showed a “lamination or parallel 
arrangement of the crystals indicative of some phase of sedimentary 
origin”; and (2) an iron-bearing group, in which he placed the 
various types of rock more or less closely associated with the iron- 
ore; and finally, (3) a gneissic and schistose group, in which he 
included the rocks with distinctly banded and foliated habits. A 
detailed discussion of the various groups and of their structure, with 
notes on the lithology, is included in this report, which is well 
illustrated with cross sections, maps and diagrams. 
The magnetite mines of southeastern New York had never been 
so carefully studied or so well described as those in the Highlands 
of New Jersey, although several were in successful operation. 
Wendt’s ?* brief description of the mines of Putnam county, New 
York drew some attention to the district, and it was about this time 
also that the Tenth Census report, previously referred to, appeared 
in print. 
Wendt ** discussed the general characters of the ores, the methods 
of mining and the production, and gave outline diagrams of both 
the Mahopac and Tilly Foster ore bodies, showing the offset in the 
latter at the 110-foot level produced by faulting,?* but beyond a 
statement that “ geologically the occurrence of the ore is a counter- 
part of that of the New Jersey and Lake Champlain magnetites,” 
no hypothesis as to origin was ventured. Ruttman,”* however, was 
very much more specific in his statement, for he said, “ The ore- 
body at Tilly Foster is without doubt a bed, the ore having been 
deposited, whatever its original state, simultaneously with the strata 
of gneiss which form a large part of the surface rock of Putnam 
county” (p. 80), and a mental picture of the processes operating to 
produce such a deposit was not lacking, for “ This ore-sediment was 
probably derived from preceding formations and carried in 
mechanical suspension by streams or torrents, into a basin or depres- 
sion of the rock-sediment formed just previously, the deposit of 
ore being then covered by layer on layer of rock-sediment until, by 
accumulated pressure and heat, the rock-sediment was changed to a 
21 Wendt, A. F. The Iron Mines of Putnam County, New York. Trans. 
Am. Inst. Min. Eng., v. 13. 1885. 
22 Op. cit. | 
23 Major T. B. Brooks first suggested this structure. See Tenth Census 
Report, 1880, p. 103, footnote. 
Putnam suggested as an alternative explanation that the ore body of the 
Tilly Foster might be concentrated along the axis of a compressed and over- 
turned anticlinal fold pitching northeasterly and possibly faulted on the line 
Olmtlisnass 
24Ruttman, F. S. Notes on the Geology of the Tilly Foster Ore Body, 
Putnam County, New York. Trans. Am. Inst. Min. Eng., v. 15. 1887. 
