418 W. J. MILLER ADIRONDACK ANORTHOSITE 



syenite-granite series^ not nearly so great a thickness need be assumed. 

 On this view a vertical thickness of fully 3,000 feet is actually exposed in 

 Mount Whiteface, and how much more should be added to make up for 

 the upper portion removed b}^ erosion is of course unknown. Probably 

 little or none is to be added to the bottom, because Marcy anorthosite out- 

 crops near the base of the mountain. 



The Schroon Lake quadrangle yields similar evidence, since, as above 

 pointed out, the border facies (Whiteface anorthosite) there formerly 

 extended fully 7 or 8 miles out beyond the present margin of the Marcy 

 anorthosite, as indicated by numerous inclusions in the syenite-granite 

 series. In this connection a very interesting inclusion of typical Marcy 

 anorthosite in the granite, over 6 miles out from the present border of 

 that anorthosite, may be reasonably interpreted as a fragment caught up 

 in the granite magma at a lower level (below the Whiteface anorthosite 

 cover) and carried upward to its present position. In any case it is cer- 

 tain that Marcy anorthosite existed that far out. Within the Schroon 

 Lake quadrangle I found no Whiteface anorthosite within the large area- 

 of Marcy anorthosite there exposed. ■ 



Kemp^s Elizabethtown map shows a prominent belt of gabbroid border 

 anorthosite extending several miles northward into the Marcy anorthosite 

 country and to an unknown distance into the adjoining quadrangle. This 

 belt may be plausibly explained as a remnant of a once widespread cover 

 over at least the outer portion of the great body of Marcy anorthosite. 

 That this border facies once extended considerably farther beyond the 

 present limits of the continuous body of anorthosite is proved in two 

 ways, namely, by the occurrence of the two large inclusions of border 

 anorthosite well within the syenite and by the complete cutting out of the 

 border by the syenite in places. 



Cushing's Long Lake map represents one small area of gabbroid border 

 anorthosite surrounded by Marcy anorthosite more than a mile in from 

 its margin. 



Unless definite areas of this basic chilled border facies are found far 

 within the great anorthosite area, positive proof that such a border facies 

 once existed as a cover over the whole will be wanting. But such a border 

 facies, if once present as a universal cover, would show few, if any, re- 

 mains far within the great anorthosite area because of the widespread and 

 deep erosion to which the region has been subjected. 



In short, the evidence from the outer portions of the great anorthosite 

 body strongly supports the view that a chilled gabbroid border facies 

 should be regarded as having formerly existed as a cover resting directly 

 on the whole mass of Marcy anorthosite. The evidence from the interior 



