MAGNETITE IRON DEPOSITS OF SOUTHEASTERN NEW YORK 25 
appears to have been in such a condition that subsequent to its 
formation it was able to move as a mass and to a moderate extent 
invade the surrounding rocks in the form of small dikes or veins.” 
(op. cit., p. 24.). A. C. Spencer," who studied the Precambrian 
geology of the Franklin Furnace area likewise found it difficult to 
determine the exact origin of the magnetite, although an igneous 
origin is favored; in his discussion of the origin of the ore deposits 
Spencer states: “The ore deposits of the Highlands region offer 
in themselves no adequate clues for determining their origin, and the 
best that can be done in this direction is to assign the deposits to the 
most probable place in the geologic history of the Precambrian rocks. 
As the history of these old rocks is obscure, the genesis of the ores 
can be considered only in very general terms. . . . The magnetite 
ores of the Highlands are believed to have been formed by igneous 
processes connected with the invasion of the region by the granitoid 
rocks which are characteristic of the Precambrian area.” (p. 8.) 
Like Bayley, Spencer believed the Losee and Byram gneisses to be 
of igneous origin and considered the gneissic foliation to be an 
original structure in the invading rocks of the Precambrian com- 
plex. He believed that crystallization-differentiation would not only 
account for the difference in composition between the Losee, with 
sodic feldspar, and the Byram gneiss, whose feldspar is dominantly 
potassic, but would also provide for the production of metamorphism 
in the Pochuck gneiss and the Franklin limestone. The differentia- 
tion hypothesis, according to Spencer, also suggests a method by 
which notable deposits of iron and zinc ore have been segregated. 
It was about this time that Henry B. Kitimmel, state geologist of 
New Jersey, requested William S. Bayley to prepare a report cover- 
ing the entire history of the iron-mining industry in the state. 
The report,°* issued in 1910 as a volume of 500 pages, contains a 
review of all the literature pertaining to the subject and complete 
descriptions of all the ore bodies in the state. It is well illustrated 
with maps and diagrams, it contains good descriptions of the 
structural features of the gneisses and of the ore, and it is a valuable 
contribution to the general and to the economic geology of the 
Highlands region of New Jersey. With respect to the origin of 
the New Jersey magnetites Bayley says: “It is quite evident from 
the character of the different types of ore that they have all had the 
—_ 
61 Folio 161, U. S. G. S., Franklin Furnace Quadrangle. 1908. Folio 2, 
Geol. Atlas of N. J., 1908. 
62 Bayley, W. iS. Iron Mines and Mining in New Jersey, v. 7, of the 
Final Report Series of the State Geologist. Trenton, 1910. 
