430 W. J. MILLER ADIRONDACK ANORTHOSITE 



and has pushed its way through a schist conglomerate containing pebbles 

 and boulders of quartz-porphyry, sandstone, green schist, and occasion- 

 ally also anorthosite quite like some facies of the adjoining mass. Ap- 

 parently a long interval separated the anorthosite eruption from that of 

 the anorthosite." Not only is this granite distinctly later than the anor- 

 thosite, but also there is no evidence of gradation of anorthosite into 

 granite or even syenite. 



BROAD INTRUSIVE TONGUES OF SYENITE AND GRANITE IN ANORTHOSITE 



The broad tongues of syenite and granite extending, in a number of 

 places for miles, into the great body of anorthosite furnish perhaps even 

 more impressive evidence than the dikes that the syenite-granite series is 

 really younger than the anorthosite. 



Eegarding an excellent example of such an intrusion of syenite into 

 the anorthosite of the Long Lake quadrangle, Cushing^^ says: "It cuts 

 into the anorthosite for a depth of 2 miles, cutting out much of the gab- 

 bro -and anorthosite-gabbro border, though these appear in full width on 

 both sides of the salient.'' This intrusive tongue is from 1 to 3 miles 

 wide. 



In the Schroon Lake quadrangle I have mapped a tongue of granite 

 from 2 to 4 miles wide which extends into the anorthosite for fully 4 

 miles, reaching all the way through the border facies and into the Marcy 

 anorthosite. A large intrusive mass of still later gabbro appears within 

 this salient. In two places I have found small dikes as offshoots of the 

 salient sharply cutting the anorthosite. 



My Lake Placid map shov\^s a fine example of a tongue of syenite grad- 

 ing into granite and extending for several miles into the Whiteface anor- 

 thosite across the southern portion of Wilmington Mountain. On the 

 south a considerable body of Grenville lies in contact with this intrusive 

 tongue. This tongue, with a width of 1% niiles on the w^est, gradually 

 becomes narrower toward the east, till finally it sends the dikes of syenite, 

 already described, into the anorthosite. 



A great body of syenite, with locally developed granitic facies, varying 

 in width from 1 to 6 miles, extends into the anorthosite area 13 miles 

 across the Lake Placid quadrangle, and thence for an unknown distance 

 into the Mount Marcy quadrangle. I confidently believe this to be intru- 

 sive into the anorthosite, my reasons being stated beyond in this paper. 

 This big tongue of the syenite-granite series extends much farther into 

 the great body of anorthosite than any other thus far mapped in detail. 



I 



37 H. P. Gushing : Jour. Geol., vol. 25, 1917, p. 506. 



