MAGNETITE IRON DEPOSITS OF SOUTHEASTERN NEW YORK 69 
a slightly different conception of the processes which were 
responsible for the deposition of the magnetite. 
As early as 1897, J. F. Kemp*” concluded that some of the 
Adirondack magnetites were of igneous origin; he described the 
magnetite deposits at Port Henry, N. Y., as “ contact deposits formed 
by the influence and stimulus of the gabbro intrusion. Attendant on 
their (1.e., the gabbros) cooling and crystallization, the emission of 
highly heated solutions of iron and other compounds transpired, 
presumably with vapors in some degree, and these circulating along 
the various contacts gave rise to the ore bodies. They must have 
replaced in large part the wall rocks and have made a place for the 
iron oxide in this way.” This is an exceedingly shrewd observation, 
the significance of which has been overlooked or neglected by those 
who have made later studies of the Adirondack magnetites, and 
similar deposits elsewhere. Kemp and Newland *™ 11 years later, 
and with additional study, still remained convinced that these ore 
bodies were derived from igneous sources. 
Miller “° likewise ascribes an igneous origin to the magnetites (of 
Clinton county), but his conception of the source of the magnetite 
seems to be at variance with the evidence presented by a study of 
the deposits in southeastern New York. According to Miller (op. 
cit.), the magnetite of Clinton county is a product of the transforma- 
tion of the hornblende and hypersthene of the older gabbro and 
metagabbro, into diallage, of lower iron content, through the action 
of the invading pegmatites. 
The slight loss in iron which the hornblende and hypersthene 
would suffer by such paramorphic change postulates the assimilation 
of inconcetvably enormous amounts of gabbro in the invading 
granite in order to account for the great deposits of magnetite 
which are known to exist. There is no evidence, in the Highlands 
of southeastern New York, that any such process was ever opera- 
tive; so far as the Adirondack deposits are concerned, Newland’s *° 
criticism of Miller’s conception seems justified. 
The New Jersey magnetites are likewise igneous in origin, accord- 
3 Kemp, J. F. Geology of the Magnetites near Port Henry, N. Y. 
Ideas, AN I, IMI By) a7e 146-203. 1897. 
114 Kemp, J. F.. & Newland, D. H. Geology of the Adirondack Magnetic 
Iron Ores. N. Y. State Mus. Bul. 119. 1908. 
115 Miller, W. J. Magnetic Iron Ores of Clinton County, N. Y. Econ. 
Geol., v. XIV, Pp. 500-35. I9I9. 
S103 Discussion of Miller’s paper by D. H. Newland. Econ. Geol., 15, p. 177- 
. 1920. 
