THE ANORTHOSITE BODY IN THE ADIRONDACKS 511 



at higher horizons in the Grenville, though much of it remained 

 substantially where generated — enough, perhaps, to justify the 

 statement that the Adirondack complex is "essentially a sheetlike 

 mass with syenite overlying anorthosite." Whether distant syenite 

 masses are to be regarded as related to the anorthosite I cannot say. 



As a consequence of reintrusion, invasion of the anorthosite 

 by syenite, in so far as this occurs, is especially likely to be true of 

 the basic border phase, the anorthosite-gabbro or gabbro, and, after 

 the manner of the acidic phases in the Palisade intrusive, it may be 

 expected that the syenite will exert a strong corrosive or resorbing 

 action on these basic differentiates, such as that described by 

 Professor Cushing from Long Lake. While, therefore, the syenite 

 would be pushed up from below into and beyond the basic phase 

 of the anorthosite, it is considered that the syenite came into being 

 at a higher level than the anorthosite proper. This is not incon- 

 sistent with the occasional occurrence of dikes of syenite in the 

 anorthosite, for a splitting of the solidified anorthosite would permit 

 the formation of such dikes from an overlying liquid syenite as 

 readily as from a deeper-seated mass. Professor Cushing is able 

 to bring into court more examples of these dikes than I had supposed 

 were known, but I think that it must be admitted that in much 

 of the quadrangle work the syenite is considered later than the 

 anorthosite solely on the basis of his findings in the Long Lake 

 quadrangle. This might be considered as due to failure of exposure, 

 but in the same areas there is no lack of evidence of the invasion 

 of the Grenville by syenite. I consider it likely, therefore, that 

 the syenite does not invade the anorthosite in exactly the same way, 

 but is largely transitional into it, although, being of somewhat later 

 consolidation, it may send dikes into the anorthosite on occasion. 

 My observations are admittedly limited, but I do not think that 

 the intermediate types to be seen at Lake Placid are formed by 

 interaction of the two types, an action of which Professor Cushing 

 finds abundant evidence at Long Lake. The Placid types are quite 

 definitely intermediate between syenite and anorthosite, not 

 between syenite and gabbro, as are Cushing's reaction types. 



In conclusion, I would state that, while Professor Cushing has 

 raised legitimate objections and there is certainly room for difference 



