614 WILLIAM J. MILLER 



the frequent very notable variations in strike, often within relatively 

 small areas, to be accounted for ? 



According to the general principles outlined in connection 

 with the foregoing discussion of the syenite-granite series, it is the 

 writer's conception that the foliation and granulation of the anortho- 

 site were developed essentially by flowage or other movements in 

 the magma under moderate pressure, mostly just prior to its com- 

 plete consolidation. As Cushing has said regarding the Long Lake 

 quadrangle anorthosite: "In some portions of the rock the feldspar 

 crystals are more numerous, are smaller and are all arranged with 

 their long axes parallel. This is a 'flow structure' due to move- 

 ments in the mass during solidification." 1 The better foliated or 

 better granulated belts throughout the great mass represent merely 

 places where the magmatic currents or other movements were more 

 pronounced. The coarser-grained portions would of course have 

 undergone less complete granulation, but coarseness of grain and 

 absence of dark minerals would not necessarily have tended to 

 prevent the development of foliation. Thus, in the Broadalbin, 

 North Creek, and Lake Pleasant quadrangles the writer has 

 observed coarse granite-porphyry, almost free from dark minerals, 

 with highly gneissoid structure due to thorough flattening out of 

 both quartz and feldspar, while in other cases the porphyry shows 

 little or no foliation. It would seem, therefore, that the general 

 absence of foliation throughout so much of the anorthosite is best 

 explained as the result of the much more uniform intrusion of this 

 single great body which is less involved with Grenville masses, or, 

 in other words, to much less forced differential flowage. Because 

 of its great size, the pressure due to shouldering effect on adjacent 

 rocks would be relatively slighter toward the interior of the 

 mass. 



Not only is the foliation well developed around the margin of 

 the great intrusive, but it also appears to be especially well exhibited 

 in man}' parts of the area in the gabbroic fades where they are close 

 to masses or inclusions of Grenville. Just as flow structure is often 

 best shown close to the wall-rock of, or an inclusion in, a small 

 intrusive body, probably because of friction against the wall-rock 



1 H. P. Cushing, New York Stale Mus. Bull., No. 115, 1907, p. 472. 



