MAGNETITE IRON DEPOSITS OF SOUTHEASTERN NEW YORK 33 
in a northerly direction. . . . The Sterling Hill deposit, like that 
of Mine Hill, is a layer in the form of a trough. . . . Although 
there is no direct evidence to show whether the ore layer was first 
deposited and then bent into its present shape, or whether it was 
formed along a previously folded stratum or fissure, the latter is 
regarded as the more lkely.’ ** 
Forty years previous to this a cross-section of the ore body in the 
Hurdstown mine was depicted by Doctor Cook *? showing an over- 
turned asymmetric synclinal fold, or at least a structure which 
strongly resembles such a fold; Doctor Cook also mentions other oc- 
currences of like nature. Nason likewise described folded struc- 
tures in the iron mines at Ringwood, N. J., and other geologists who 
worked in the New Jersey Highlands have observed similar phenom- 
ena. The forms of the ore bodies of the Forest of Dean mine (fig. 3) 
and of the Scott-Cook-Augusta group in southeastern New York are 
suggestive of inherited folded structures, and the curving strike of 
the hornblendic gneiss on the east, south and west of Sterling lake 
(fig. 6) might be interpreted as being due to the intersection of a 
parabola-shaped, northeastwardly pitching, asymmetric, synclinal fold 
with an erosion plane, namely, the surface. Moreover, the crystalline 
limestone of Sprout Brook valley is judged by Berkey ™ to represent 
an infolded belt of very old Precambrian age, the valley in which it 
lies being synclinal with a gentle southwestwardly pitch. There 
seems to be no doubt, therefore, that structures other than mono- 
clinal are prevalent in the Highlands, ‘but that in most cases these 
structures are somewhat obscure. 
Provided the exposures showing the general steep southeast- 
wardly dip (the so-called “ monoclinal structure”) of the gneisses 
be regarded as the eroded edges of large folds, then folding is every- 
where plainly evident, the more obscure features being those already 
mentioned ; and in addition occasional cross foldings which tend to 
offset and to produce embayments in the gneiss ridges, to change 
the courses of streams as they follow the curving strike of the softer 
rock, and to produce “rolls”? such as those which occur in the 
vicinity of Sterling lake and which influence the shape of the ore 
bodies in the Lake and in the Sterling mines. These “rolls”’ were 
81U. S.G. S. Folio 161. Franklin Furnace Folio, N. J. 1908, p. 24-and 25. 
Italics are the writer’s. 
82 Cook, G. H. Geology of New Jersey, Newark, p. 58. 1868. 
83 Nason, F. L. The Geologic Structure of the Ringwood Iron Mines, 
New Jersey. Trans. A. I. M. E., 24: 505-21. 1804. 
84 Berkey, C. P. Structural and Stratigraphic Features of the Basal 
Gneisses of the Highlands. N. Y. State Mus. Bul. 107, p. 370. 1907. 
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