MAGNETITE IRON DEPOSITS OF SOUTHEASTERN NEW YORK 49 
nated and injected by magmatic material. Xenolithic masses and 
roof-pendants maintaining the regional strike, swamped in the 
invading igneous units, are commonly all that remain of the meta- 
morphosed Grenville sediments in the area under discussion. In 
some places, however, interbedded limestones and limestone beds, 
now highly metamorphosed crystalline dolomites, seemed more 
resistant to lit-par-lit injection than the associated schists, and 
accordingly were less affected and better preserved. Such, for 
example, as the Sprout Brook limestone in Putnam county, the 
interbedded crystalline limestone just west of the Forest of Dean 
mine in Orange county which pitches under Lake Popolopen, and 
other occurrences of crystalline dolomite in the same region. In 
general, however, the Grenville is represented by detached masses 
swamped in later igneous intrusives. 
The most striking and most important thing in connection with 
the Grenville is the evidence of strong structural control which this 
metamorphosed series of ancient sediments exerted on the later 
magmatic units which invaded it; for not only were the banded 
gneisses produced by the soaking and Jit-par-lit injection of the 
Grenville schists, but the shapes and structures of the ore bodies 
themselves were in large part inherited from the rock which, by 
magmatic processes, was replaced by magnetite. 
The term “ Grenville,” therefore, is used in this discussion to 
designate the highly metamorphosed, folded series of schists, quartz- 
ites, crystalline dolomites, interbedded crystalline dolomites and 
amphibolites of “Archaeozic’’ time, only remnants of which, in 
unmodified exposures, now exist. 
POST-GRENVILLE, EARLY PRECAMBRIAN IGNEOUS 
INTRUSIVES 
The Pochuck. The earliest of the magmatic units to intrude 
the Grenville series was a basic igneous magma which is now repre- 
sented in its simplest form by material with the general composition 
of pyroxenite, although it varies slightly from place to place and is 
very limited in extent and distribution. Part of the footwall of an 
open cut leading into the slope of the Clove mine *’ is hornblende 
pyroxenite, the hanging wall being in part hornblendite (plate 1). 
The footwall of the Red-back mine is in part pyroxenite and 
pyroxenite may be found on the dumps of the Upper California, 
97 The mine itself is full of water and inaccessible. The same condition 
prevails in all the old mines, and in most of the open cuts. 
