38 NEW YORK STATE MUSEUM 



one-half of a mile. The origin and relations of this rock are not 

 clear to the writer. 



The main bulk of the rock is decidedly like the syenite in appear- 

 ance, being medium grained nonporphyritic, moderately to very 

 gneissoid, greenish gray where fresh, and weathering to brown. In 

 the small quarry by the road near the southern end of the area, this 

 type of rock is finely exposed. No. 32 of table 2 represents a thin 

 section of rock from the quarry. No. 40, which represents a thin 

 section of similar rock from the shore of the river 1)4, miles 

 farther north, is exceptional in being pinkish gray, probably due 

 to weathering. Compared with the normal syenite, the average 

 amount of plagioclase in this so-called basic phase of the syenite 

 is seen to be higher. Thus the rock is more basic, being more like 

 diorite than syenite. In every other way, however, the rock shows 

 strong syenitic affinities. 



Whether this so-called basic phase of the syenite is merely a 

 differentiation phase of the adjacent normal syenite, or is a product 

 of assimilation of some anorthosite by the syenite magma, the writer 

 can not say. Its situation between the Keene gneiss (below 

 described) and syenite strongly suggests the latter possibility. If 

 the rock is an assimilation product it may be regarded as a sort 

 of nonporphyritic outer zone of the Keene gneiss where the latter 

 shades off into the normal syenite. In the field the relation of the 

 rock to the Keene gneiss could not be positively determined because 

 of lack of exposures along the border. Very similar rocks, usually 

 regarded as basic differentiation phases of the normal syenite, are, 

 however, known from various parts of the Adirondacks. 



Granitic syenite. This rock is clearly intermediate between 

 the normal quartz syenite and the granite or granite porphyr}''. It 

 is an acidic facies of the syenite in which the quartz content is 

 about 20 to 25 per cent. Since nothing like sharp boundaries exist, 

 this percentage of quartz is only approximately represented in the 

 twelve areas indicated on the geologic map. These areas, well 

 scattered over the quadrangle, do not occupy more than 5 or 6 

 square miles. The rock is in every way much like the normal quartz 

 syenite except for higher quartz content and frequent tendency to 

 weather pink or pinkish gray. 



On the eastern shore of Buck island in Lake Placid, where the 

 pegmatite dikes cut the granitic syenite, the latter contains as much 

 as I per cent of graphite in small flakes (see no. 31 of table 2). 

 Since this granitic syenite is here closely associated with small 



I 



