MAGNETITE IRON DEPOSITS OF SOUTHEASTERN NEW YORK 51 
syenitic facies of the Pochuck proper, which invaded, soaked, pene- 
trated, and thoroughly impregnated the previously folded and meta- 
morphosed Grenville sediments; and in part to (0) the strong struc- 
tural control exerted by the folded and metamorphosed sediments on 
the invading igneous magma, so that the original foliated habit of 
the Grenville, and in large part even the folded structures, were 
retained, or inherited, by the mixed resultant of the intrusion. The 
dark, coarse, strongly foliated and streaked, strongly biotitic and 
hornblendic rocks arising from this process have been called “ horn- 
blendic gneiss” by the older geologists, and “ Pochuck Gneiss ” °° 
by the geologists working in the adjacent Highlands area in New 
Jersey. 
The writer believes both field and petrographic evidence indicates 
that the impregnation and “soaking” of the Grenville was the 
earliest expression of magmatic invasion by the Pochuck; that the 
unmixed exposures of igneous origin already mentioned, with the 
associated pegmatites, represent the closing stages of such invasion, 
and in that sense later; that the pegmatites and the associated mag- 
netite are differentiation products concentrated in essentially aqueo- 
igneous solution and as an elimination residuum produced through 
the action of selective crystallization; and that the extreme, ultimate 
end product of this action was quartz with more or less soda-feld- 
spar, which in the immediate vicinity of the ore bodies is found in a 
purer form as a very coarse quartz-feldspar granite (Pochuck 
granite), but which is rather widely distributed involved with 
Pochuck-Grenville. (Plates 2, 3 and 4 illustrate the types.) 
Modified Pochuck-Grenville. In many places the mixed, 
strongly foliated, highly biotitic or hornblendic Pochuck-Grenville 
has been further modified by lit-par-lit injections of lighter colored 
feldspathic or granitic matters, combined in some cases with 
epidote, with the consequent production of banded injection- 
gneisses, epidote gneisses and granitized products; these modified, 
injected and banded rocks are highly complex in structure, history 
and origin, but nevertheless perfectly understandable provided one 
follows their development step by step as resulting through the 
SNVoliinnauieancc brooks Aa Hew Toth Annals mept) We Sy GaSe) pt lil 
1896-97; Washington, 1808; p. 440. The name “ Pochuck” was first used 
by these writers in describing the rocks of Pochuck mountain. See also, 
Bayley, W. S., Iron Mines and Mining in New Jersey, v. 7 of the final 
report series of the Staté Geologist, 1910; Geologic Folios, U. S. G. S. 157, 
161, 191, and Folios 1 and 2, Geol. Atlas of N. J. 
