24 NEW YORK STATE MUSEUM 
cutting all the other rocks, and magnetite closely associated with it. 
Spencer thought the streaked and foliated structure of the gneisses 
to be original, due to flowage while the rocks were not completely 
consolidated. He concluded the magnetites to be likewise of igneous 
origin and to be connected with the invasion of the pegmatites. 
“Instead of being bog ores, or carbonates deposited in sedimentary 
rocks and later changed to magnetite by metamorphism, as formerly 
suggested, they have been apparently introduced as products of 
igneous activity. The process suggested, however, must not be con- 
fused with magmatic differentiation as commonly understood.” ” 
Since the pegmatites are generally thought to have been formed by 
the crystallization of silicate minerals from what must have been 
essentially an aqueo-igneous solution, and since the magnetites are 
closely associated with the pegmatites, Spencer conceived that the 
magnetite ore bodies must likewise be related to end-phase con- 
solidation processes. ‘‘ The process is not regarded as one of mere 
separation and bunching of dark silicates and magnetite within 
masses of crystalline rock originally containing the required elements 
in the necessary proportion ; but it is conceived that the accretion of 
certain substances, such as the iron oxide, was brought about by the 
addition of material dissolved in magmatic waters which permeated 
and moved through the pasty pegmatites as long as they were in an 
unconsolidated condition.” (op. cit.) There is thus here recorded 
a new conception of the origin of the magnetite which seems to be 
much more in accordance with field relations and occurrences than 
the older ideas of previous workers in this area. 
Four years later, W. S. Bayley,°° in his description of the Pre- 
cambrian geology of the Passaic quadrangle, postulated an igneous 
origin for the Losee and Byram gneisses, and for part of the 
Pochuck gneiss (p. 5, op. cit.) ; but while concluding that the 
magnetite associated with the pegmatites was an essential part of 
the rock, and hence igneous, Bayley left the origin of the remaining 
ores in doubt. Thus, in discussing the magnetiferous phases of the 
Pochuck gneiss he remarks: “If the Pochuck is metamorphosed 
sedimentary material the masses of ore must also be a metamorphic 
product. It does not necessarily follow, however, that the iron must 
have been in the originalsediment!”)” <2) 2) he iron here may 
have been introduced by hot circulating solutions under conditions 
of igneous metamorphism. Whatever the origin of the ore, it 
59 Mining Magazine, v. 10. 1004. 
60 Folio 157, U. S. G. S., 1908. Also Folio 1, Geol. Atlas of N. J. 
