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W. J. MILLER ADIRONDACK ANORTHOSITE 



It seems evident from a glance at my Schroon Lake geologic map that 

 the anorthosite once extended out as a continuous broad belt at least 7 or 

 8 miles beyond the present margin of the Marcy anorthosite, because 

 within that distance from the Marcy anorthosite there are many inclu- 

 sions of anorthosite (many of sufficient size to be mapped) in the syenite- 

 granite series all the way across the quadrangle. In other words, only 

 mere remnants of the former anorthosite here remain. With the excep- 

 tion of one locality, these are all inclusions of Whiteface anorthosite. 

 The exceptional locality is of particular interest. It is on top of the 

 small mountain of typical granite a little over a mile north-northeast of 

 Pat Pond. One* patch of the granite 12 feet across contains large dark 

 bluish gray labradorites an inch or more across and several small pieces 

 of typical Marcy anorthosite as distinct inclusions mostly arranged 

 roughly parallel to the foliation of the granite. Immediately around the 

 larger fragments the granite shows fine magmatic flow-structure. A sim- 

 ilar exposure occurs close by. My interpretation is that the granite 

 magma moving upward enveloped two small masses of Marcy anorthosite 

 and tore them into small fragments, which became somewhat • scattered 

 and arranged parallel to distinct magmatic currents, which worked its 

 way up nearly vertically, as shown by the high angle of dip of the flow- 

 structure foliation. 



In the Schroon Lake quadrangle several inclusions of Whiteface anor- 

 thosite bear exactly the same relation to the inclosing syenite-granite 

 series as neighboring inclusions of Grenville, and it seems clear that the 

 upward moving syenite-granite magma enveloped masses of both of these 

 rock types in exactly the same manner. 



A very fine display of many inclusions of fragments of Whiteface anor- 

 thosite of all sizes occurs in typical granite on Cobble Hill, 1 mile due 

 south of Bailey Pond, in the Schroon Lake quadrangle. A wide zone 

 fully one-fourth of a mile long in the granite contains the inclusions, 

 most of which are arranged parallel to the foliation of the granite (see 

 figure 2). 



Inclusions of Whiteface anorthosite in the syenite-granite series were 

 also observed by me in a nuitiber of places in the Lake Placid quadrangle. 

 A few will be described. Ledges of syenite by the river one-fourth of a 

 mile east of High Fall contain inclusions of the Whiteface rock arranged 

 parallel to the foliation of the syenite. Similar inclusions occur in sye- 

 nite by the river one-half of a mile southwest of The Flume and also on 

 top of the hill in the area of mixed gneisses 2^ miles north-northeast of 

 Keene. An 8-foot boulder of syenite, in the bed of the river about a mile 

 northeast of High Fall, contains several very distinct inclusions of White- 



