MAGNETITE IRON DEPOSITS OF SOUTHEASTERN NEW YORK 63 
structure occurs in the Red-back mine, and along the line of pits 
known as the Steele mine. The roll structure is not confined to the 
mines, however, but is a more or less constant structural feature 
in the area which includes the Sterling group, the Scott group, the 
Red-back belt, and the Bering and Morehead mines. 
The strikes of the axes of the rolls are variable, but in general at 
greater or less angles to the regional strike of the rock. They 
resemble small folds with very short axial directions and extremely 
steeply dipping limbs, spaced but a short distance apart from crest 
to crest; they appear to be corrugations produced by minor cross- 
folding in a previously folded series of strata. They are confined 
to the Pochuck-Grenville, and may be explained as localized cross- 
corrugations produced during the injection and impregnation of the 
folded Grenville strata by the earliest basic intrusive, the Pochuck. 
They are believed to antedate the pegmatitic differentiates of the 
Pochuck magma, and the ore. The form of the ore bodies is in 
part controlled by the rolls where they are especially prominent (see 
figure 5), and the reason why they are such striking structural 
features in the Lake and Sterling mines 1s probably because those 
ore bodies lie in the spoon-shaped end of a pitching syncline, where 
cross-folding would be especially effective in producing a series of 
corrugations with diverse axial directions. 
Faults. The complex faulting of the Highlands region has been 
discussed in part 1. Notwithstanding the numerous faults of both 
Appalachian and Triassic types, the main ore bodies are surprisingly 
little affected. The faults cutting the magnetite deposits are chiefly 
normal faults of Triassic age, whose horizontal displacements are 
generally toward the hanging wall side (or toward the right, when 
facing northeast). 
Both vertical displacement, or throw, and lateral displacement, or 
heave, are usually small in amount; the fault-planes generally dip 
very steeply, and the faults usually cross the ore bodies at high 
angles to the strike of the ore. The Forest of Dean ore body is 
unaffected by faulting, as is the main body of the Lake mine, pro- 
vided the zone judged by the writer to be a healed, Precambrian, 
preore fault zone, is excepted. This is described in part 4, in the 
description of the Lake mine, as the “ slip-zone.” The extreme 
southerly tip of the Sterling ore body seems to have been cut by a 
normal fault which strikes approximately north 60° east. The west- 
erly extension of this fault appears to be responsible for the offset of 
the lower ore-horizon along which lie the Summit, Upper California, 
