50 NEW YORK STATE MUSEUM 
Crossway, Parrott, and O’Neill mines. Intimately connected with 
the basic phase and probably derived from it by differentiation 1s an 
extensive series of pegmatites whose compositional range varies from 
dioritic to syenitic, with which is associated the magnetite. The 
pegmatites occur in all textural gradations from coarse, highly 
feldspathic, typical pegmatites of dioritic, monzonitic and syenitic 
compositions, to granitoid rocks which are essentially diorites and 
syenites, but which grade erratically into coarser and more typical 
pegmatitic facies in places. These are always most intimately asso- 
ciated with one another and with the magnetite, and are therefore 
especially prominent in and around the mines, forming in every 
instance parts of the wall of the ore bodies (see plates 2 and 3). 
The dioritic facies of the Pochuck is characterized by a brilliant 
green pleochroic pyroxene, plagioclase feldspar ranging from oligo- 
clase to andesine, magnetite in end-phase consolidation relationship, 
with occasionally antiperthite and quartz as minor components. 
The syenitic facies of the Pochuck in many cases might well be 
regarded as a more acid varietal phase of the dioritic facies. The 
feldspars are chiefly, and in some cases wholly, acid plagioclase 
ranging from albite to albite-oligoclase; if perthite appears it is 
usually antiperthite. Quartz not infrequently is present as an acces- 
sory mineral, and titanite as a rather prominent accessory is common 
to both the syenitic and dioritic phases of the Pochuck. 
Provided these two types are classified on the basis of dominant 
plagioclase, regardless of its composition, then both these varietal 
facies of the Pochuck may properly be called diorites; if on the 
other hand a division is made on the basis of dominant alkali feld- 
spar (albite) as contrasted with dominant calci-alkalic feldspar 
(oligoclase-andesine), then the albite-rich variety may properly be 
considered a soda-syenite; these are the distinctions made by the 
writer. 
By the term “ Pochuck,” therefore, is meant the unmixed igneous 
phase of the earliest basic intrusive into the Grenville series. As 
used by the writer the term includes pyroxenite, hornblendite, 
peridotite, diorite, soda-syenite, the associated extensively developed 
pegmatites with their co-related magnetites, and a peculiar coarse 
“oranite,” later described. 
The “ Pochuck-Grenville.” The most extensive development 
of the “ Pochuck” is not simple, unmixed igneous rock, but a mixed 
Grenville-Pochuck type which owes its character in part to (a) the 
powerfully penetrating and “soaking” ability of the dioritic and 
