MAGNETITE IRON DEPOSITS OF SOUTHEASTERN NEW YORK 29 
Fenner,’* as a result of his study of certain of the gneisses in the 
Highlands of New Jersey attached much importance to the con- 
trolling influence exerted by the structures in the Precambrian sedi- 
ments: “Evidence is given leading to the belief that the structures 
at this locality (northern New Jersey) can not well be attributed to 
the squeezing-out of a partly differentiated magma or to the shearing 
and recrystallization of a solidified rock, but that their origin must 
be looked for in a process involving the injection of a thinly fluid 
granitic magma between the layers of an original rock of laminated 
structure. . . . The observed relations are very similar to those 
which French geologists have described under the name of Iit-par-lit 
injection, and the mode of operation is believed to have been 
essentially the same.” (p. 701-2) 
But while Bayley, in his discussion of the Precambrian geology 
of the Raritan, N. J., quadrangle states: ‘The light-colored 
granitoid gneisses are undoubtedly of igneous origin. . . . Large 
amounts of preexisting rock material may have been more or less 
completely dissolved and assimilated by the invading magmas and 
some of the peculiar phases of the gneisses may be due to this fact. 
The portions of the Pochuck gneiss older than the other 
gneisses may be igneous rocks into which the later gneisses were 
intruded, or they may be old sedimentary rocks entirely recrystallized 
through the influence of the Losee and Byram magmas”’ (p. 5), no 
specific statement involving lit-par-lit injection is made, although 
6 years earlier Spencer ‘° concluded that in the case of the dark 
gneisses the “ interlayering ” of the granitoid material was so regular 
that some structural control must have been necessary. Bayley (in 
Folio 191) describes the structural features of the Highlands with 
some care; these structures are illustrated in cross-sections which 
show the great fault which separates the Precambrian rocks of the 
Highlands from the later rocks on the southeast side. The main 
structural features of the area are a series of northeast-southwest 
folds parallel to the general Appalachian structure, two series of 
great faults trending in the same direction, and a series of shallow 
cross-folds, the axes of which trend northwest and southeast. Since 
73 Fenner, C. N. The Mode of Formation of Certain Gneisses in the High- 
lands of New Jersey. Jour. Geol., 22: 594-612, and 604-702. 1014. 
74 Folio 191, U. S. G. S. The Raritan Folio, 1914; W. S. Bayley discussed 
the Precambrian geology. 
% Folio 161, U. S. G. S. Franklin Furnace Quadrangle, 1908. 
