62 NEW YORK STATE MUSEUM 
5 The evidence of lit-par-t injection and the strong structural 
control of such injections by sediments which, in order to have 
exerted such control, must have been previously strongly schistose 
and therefore highly metamorphosed, and whose foliation planes 
were inclined. Lit-par-lit injections, soaking and impregnation are 
most easily effected along planes of structural weakness, that is, 
foliation planes; it would seem therefore as though such processes 
must operate most effectually on strongly foliated, highly schistose 
and steeply dipping strata. 
6 Gneissoid structures in invading magmatic units, which repre- 
sent in part, assimilation, partial or complete, of blocks of Grenville, 
but whose products of assimilation have been very incompletely 
distributed.*°* | 
The proof of the second statement lies in the structural characters 
of the rocks associated with the iron ores. Thus, granites, both 
geneissoid and massive, dioritic phases of the Pochuck, and massive 
granites and pegmatites associated with the ore show no signs of 
ever having been subjected to compressive stresses productive of 
folding. Some of the pegmatitic facies of the Pochuck were contem- 
poraneous with the ore, and at times were overlapping so that these 
phases appear both as dikes, cutting the ore, and as interfingering 
stringers in the ore. 
Not infrequently these dikes are of considerable size, and may be 
traced on the surface for some distances. They cut the rock struc- 
tures in various directions, but in not a single instance have they 
ever been affected by folding. Moreover, the latest of the Pre- 
cambrian intrusives, basic dikes cutting the modified Pochuck-Gren- 
ville, the ore, the pegmatites, and all other Precambrian magmatic 
units, varying in thickness from a few inches to a maximum of a 
few feet, show no signs of folding. From this evidence, therefore, 
it is judged that neither Taconic nor Appalachian folding have 
affected the Precambrian crystallines or the magnetite ore bodies to 
any degree, nor have the ore and its associated rocks been subjected 
to any such process since the ore was made. It follows, therefore, 
that the third statement must be reasonably correct. 
Rolls. One of the curious structural features in some of the 
mines of the Sterling group is the undulating character of the walls 
of the ore bodies, generally more pronounced in the footwalls, and 
especially prominent in the Lake and the Sterling mines. The same 
108 Berkey, C. P. & Rice, Marion. Geology of the West Point Quadrangle, 
N. Y. State Mus. Bul. 225-26. Also private communications. 
