GEOLOGY OF THE LAKE PLACID QUADRANGLE 5 1 



either the syenite magma or the anorthosite, or both, were not hot 

 enough, or the syenite was not in sufficient bulk, to effect more 

 than shght fusion of the immediate borders of the invaded anor- 

 thosite. 



Another important fact is that, in the field, the Keene gneiss by 

 no means universally forms a narrow zone or belt with syenite- 

 granite directly adjacent on one side and anorthosite on the other. 

 A fine case in point is the eastern part of the Sunrise notch area 

 where the Keene gneiss for i]/^ miles lies between granitic syenite 

 on one side and syenite on the other. A different case is the Oak 

 ridge area which is bordered on the south by VVhiteface anortho- 

 site, and on the north by Grenville, Alarcy anorthosite and syenite. 

 How can areas of this sort possibly be explained by Bowen's 

 hypothesis, which assumes that the anorthosite was never an active 

 magma but that it was formed by sinking of plagioclase crystals 

 with the development of a transition rock (called Keene gneiss in 

 this bulletin) occupying a position distinctly intermediate between 

 the syenite-granite and the anorthosite? Is it not much more in 

 harmony with the field relations to conceive that Keene gneiss 

 magma was produced by assimilation at a lower level and then 

 rose to invade previously formed Grenville and anorthosite, or 

 moved upward flanked on either side by syenite or granite? Also 

 are not elliptical areas like those just east of Upper Jay and i^ 

 miles west of East Kilns much more satisfactorily accounted for 

 by the latter hypothesis than by Bowen's hypothesis? Again, do 

 not the inclusions of anorthosite in the Keene gneiss (see above 

 descriptions) strongly support the writer's view that the Keene 

 gneiss, in some places at least, moved upward as a true magma? 



Finally, it should be noted that the Keene gneiss accompanies 

 both the Marcy and the VVhiteface types of anorthosite, being about 

 as common with one as with the other. Within the Lake Placid 

 quadrangle, then, the temperature relations between the syenite- 

 granite and Marcy anorthosite on the one hand, and the Whiteface 

 anorthosite on the other, do not seem to have been notably different 

 during the syenite-granite intrusion. The presence or absence of 

 the Keene gneiss appears to be irrespective of whether the syenite- 

 granite borders the Marcy or the Whiteface anorthosite. 



Comparison with Cushing's southwestern Franklin county 

 basic syenite. In Cushing's report on the geology of the Long 

 Lake quadrangle, he describes a basic phase of the syenite which 

 grades into a rather fine-grained, even granular, gneissoid rock with 

 few feldspar phenocrysts, and dark minerals often equaling or 



