MAGNETITE IRON DEPOSITS OF SOUTHEASTERN NEW YORK 55 
STRUCTURAL FEATURES OF THE MAGNETITE 
Form of the ore bodies. It has been generally stated that the 
magnetite ore bodies in the Highlands of the Hudson, in the Adiron- 
dacks, and in other localities where magnetite occurs as minable 
bodies in the Precambrian crystalline rocks, are pod-shaped lenses 
or shoots with the longitudinal planes of the pods dipping parallel 
to the dip of the “layers” of the inclosing gneisses; and with the 
longer axes of the “pods” or “lenses” pitching with the pitch of 
the rock structure.*°? In some cases several “pods” or “shoots” 
lie in the same plane, edgewise one above another, separated by com- 
paratively barren rock. 
These features are illustrated diagrammatically in figure 2, which 
is a slightly modified copy of the one shown on page 24, folio 157, 
U.S. G. S. The rock immediately overlying the crest of a pod is 
called the “cap rock,’ and that underlying the pod, along the keel, 
is known as the “bottom rock.” Where two pods or shoots lie one 
above the other in the same “ vein,” the cap rock of the lower is 
essentially the bottom rock of the upper; this relatively barren rock, 
between two such lenses or pods of ore is also known as a “ pinch.” 
Pinches, however, are never absolutely barren; the ore body in some 
cases merely narrows, reducing the width to a few inches, or a few 
feet, but usually the intervening rock, or pinch, is traversed by many 
narrow stringers of magnetite which connect the lenses or pods with 
one another. The pinches may be any of the various modifications 
of the Pochuck, previously enumerated. 
The forms of the magnetite ore bodies in the Highlands of south- 
eastern New York are by no means so simple, however, and most 
of them do not conform to the podlike or lenticular-shaped deposits 
described above, except in very general details. The surface ex- 
posures of these ore bodies give absolutely no clue to the form of 
the mass of magnetite, so that the exact shapes can be determined 
only after sufficient development, or actual mining, has been done to 
outline the cross section and reveal the dimensions. 
While many of the ore bodies are essentially tabular, they are 
extremely irregular; some are warped and corrugated, like the ore 
bodies in the Lake and Sterling mines; some split and fork, divided, 
or partly divided, by blocks and horses of the country rock, which 
may be extraordinarily persistent, as in the Forest of Dean 
102 Folios 157 and 161, U. S. G. S. 1908; Geol. Atlas N. J. 1 and 2, 1908; 
N. Y. State Mus. Bul. 119, 1908. Iron Mines and Mining in N. J., v. VII. 
Final Report Series, 1910. Folio 191, U. S. G. S. 1914. Bul. 450, U. S. G. S. 
