RELATION OF ANORTHOSITE TO GRENVILLE SERIES 423 



In any case the evidence is very clear that much, if not all, the plagio- 

 clase of such nearly pure plagioclase rocks was actually in a fluid condi- 

 tion, and thus we have more proof opposed to Bowen's statement that the 

 anorthosite gives "no evidence of having been raised to the temperature 

 requisite to melt plagioclase." The rocks above described also make it 

 certain that a very appreciable amount of true anorthosite, much of it 

 very low in femic constituents, is Just as intimately associated with Gren- 

 ville as is the syenite and in exactly the same manner. The plain infer- 

 ence is that such anorthosite was once as highly fluid as the syenite. Fur- 

 ther, if so much plagioclase of such nearly pure plagioclase rock was 

 actually fluid, is it unreasonable to suppose that the great body of even 

 more impure Marcy anorthosite may once have been a true magma with a 

 liigh percentage of liquid ? 



INCLUSIONS OF GRENVILLE IN ANORTHOSITE 



Inclusions of Grenville rocks in the Whiteface anorthosite are common. 

 They comprise various kinds of the Grenville strata and range in length 

 from an inch or two to a mile or more. Excellent examples of large ones 

 occur in the vicinity of Keene and Franklin Falls, as shown on the forth- 

 coming Lake Placid geologic map. 



Mention has already been made of the great number of small inclu- 

 sions of Grenville gneiss in the nearly pure plagioclase Whiteface anor- 

 thosite of the mixed gneiss area at the southern end of Wilmington Moun- 

 tain of the Lake Placid quadrangle. Other interesting inclusions occur 

 in the walls of The Flume, near Wilmington, in the same quadrangle. 

 The rock is medium to moderately coarse grained, consists largely of 

 pinkish labradorite, through the mass of which are scattered 2 to 15 per 

 cent femic minerals, and is in places moderately gneissoid. Some very 

 distinct small, drawn out, or lenslike inclusions of Grenville pyroxene 

 gneiss occur, a careful study of which in the field having led me to the 

 suggestions that the much smaller (one-quarter to one-half inch) numer- 

 ous lenslike masses which constitute most of the femic constituents of the 

 rock are really very small fragments of Grenville gneiss v^hich were 

 caught in the intruding magma of nearly pure plagioclase anorthosite 

 and roughly arranged parallel to the magmatic lines of flowage, thus giv- 

 ing rise to the gneissoid structure. 



Inclusions of Grenville in the Marcy anorthosite are much more un- 

 common. In the Lake Placid quadrangle I have noted such in but one 

 locality, 2 miles northeast of Keene, where several sharply defined inclu- 

 sions (each several feet across) of Grenville rocks, including limestone, 

 are plainly embedded in typical Marcy anorthosite. In the Schroon Lake 



