LOO NEW YORK STATE MUSEUM 
production during the years 1914 to 1918 was 88,o00 tons. One 
of the remarkable features of the mine is the form of the ore body 
and the manner in which the form and size persist in depth. The 
chief points of interest connected with this ore body are: 
a The ore apparently occupies the trough of a synclinal fold, 
overturned to the northwest, and pitching toward, the northeast. 
b The great horse of rock which, when the mine was first opened, 
appeared on the surface in such a way as to give the impression 
that the ore existed in two parallel bands separated by barren rock. 
This horse now projects from the roof of the mine downward, divid- 
ing the mass of ore in its upper part into two lobes, so that a . 
cross section of the ore body is roughly heart-shaped (see figure 3). 
c The rock-pendant which hangs from the roof of the east lobe, 
much like another and very small horse. 
d The dikelike rock varying from 1 to 12 feet in thickness which 
runs from the east side of the horse into the hanging wall, and which 
serves, and is used, as a floor in working the ore between the horse 
and the hanging wall, in the east lobe. This has followed the ore 
down the pitch for 3300 feet. 
e Late Precambrian basic dikes of the general composition of 
Camptonites, cutting the ore in almost vertical positions. One of 
these cut the ore at such a small angle to the strike that notwith- 
standing the fact that the dike was not more than 3 to 6 feet in thick- 
ness, it was necessary to drive the slope 300 feet through dike rock 
before ore was again encountered on the other side’. The age of 
these dikes and their undisturbed condition are particularly signifi- 
cant in the interpretation of the dynamic history of the region and 
of the ore bodies. 
f Included blocks of rock in and surrounded by the ore; the 
‘unsupported structures ” of Irving ***, some of which present every 
evidence of ‘being unreplaced remnants or country rock; and finally, 
g The persistence with which the form, cross section and size 
of the mass of ore are maintained. 
These features are of such importance to an understanding of the 
deposit that the writer is constrained to discuss them, briefly, in 
their sequence; especially since the observations presented aid in 
the interpretation of the geology and origin of the magnetite in 
general. 
14aKempi jibe Amer, Jours Sciai(3) G35) pal ssleimccoun Stoltz Guyaie: 
The Forest of Dean Iron Mine, N. Y. Eng. and Min. Jour. 85: 1091-093. 1908. 
143 Irving, J. D. Replacement Ore bodies and the Criteria for their Recog- 
nition. Econ. Geol. 6: 527-61, 619-69. IQII. 
