RELATION OF SYENITE-GRANITE SERIES 429 



On the mountain spur, 1^ miles northeast of the summit of Little 

 Whitefaee Mountain (Lake Placid quadrangle), a number of tongues of 

 granite cut the Whitefaee anorthosite. The relations are very clear in 

 the big bare ledges, the dikes being small tongues of the large body of 

 granite across the southern face of Mount Whitefaee. One of these 

 tongues is only 20 feet wide, but the others are each a number of rods 

 wide at the summit of the mountain ridge. They pinch out eastward. 

 The granite is clearly gneissoid and it contains several per cent horn- 

 blende. Immediately to the south several dikes of granitic syenite, none 

 over 3 feet wide, sharply cut Whitefaee anorthosite. Most of the anor- 

 thosite cut by these dikes is white and nearly free from femic minerals, 

 and hence probably far within the border facies — that is to say, close to 

 the outer part of the Marcy anorthosite (see figure 1). 



During the summer of 1917 my work in the Schroon Lake quadrangle 

 brought to light still other examples, these all being dikes or small 

 tongues of granite, which is there the more prominent member of the 

 syenite-granite series. One of these is well shown by the road II/2 miles 

 west of Boreas Eiver, ^here a dike of granite 5 feet wide cuts rather 

 femic Whitefaee anorthosite. Another is a dike of typical pinkish gray 

 granite, 25 feet wide, 1 mile west of the summit of Sand Pond Mountain. 

 It sharply cuts Whitefaee anorthosite, which lies near, and closely resem- 

 bles Marcy anorthosite. Both dikes last mentioned are quite certainly 

 offshoots from large bodies of typical granite which in a general way cut 

 into the marginal portion of the great body of anorthosite. Still another 

 dike of granitic syenite or granite cuts Marcy anorthosite just north of 

 the summit of Texas Eidge. 



I am confident that many othes clearly defined dikes of syenite and 

 granite in anorthosite exist in the Lake Placid and Schroon Lake quad- 

 rangles, but it is difficult to locate and demonstrate their presence in such 

 a rough, densely forested country. It should be emphasized that at least 

 some of these dikes cut right into the typical Marcy anorthosite. The 

 evidence, therefore, from the dikes, that the syenite-granite series is dis- 

 tinctly younger than the anorthosite, is very strong and by no means 

 confined to the Long Lake quadrangle. 



Dresser^^ states that on the south side of the Canadian Saguenay anor- 

 thosite border syenite grades into granite which clearly cuts the anortho- 

 site, thus exactly corroborating similar evidence from the Adirondacks. 



Coleman^^ says, regarding the largest area of anorthosite in the Eainy 

 Lake district, that the granite "has sent apophyses into the anorthosite 



85 J. A. Dresser : Bull. Geol. Soc. Am., vol. 28, 1917, p. 155. 

 38 A. P. Coleman: Jour. Geol., vol. 4, 1896, p. 911. 



