24 NEW YORK STATE MUSEUM 



metagabbro (amphibolite) are involved with the syenite. In these 

 unusually good exposures the evidence strongly points to more or 

 less digestion or assimilation of some of the old gabbro by the 

 syenite magma. West of Stony Creek station the quartz syenite 

 varies to grano-syenite which contains some zones of granite par- 

 allel to the foliation. 



On the high hill 13^ miles west of Stony Creek village rather 

 typical quartz syenite varies to grano-syenite and contains some 

 more or less absorbed bands of the old gabbro. On the high hill 

 3 miles west of the same village the grano-syenite contains some 

 very local thin bands and ver}^ small lenses of amphibolite (meta- 

 gabbro?) parallel to the foliation. The northern half of this large 

 area mapped as syenite (that is the portion lying between i and 3 

 miles northwest of Stony Creek village) contains mostly medium- 

 grained, brown, well- foliated, hornblendic grano-syenite locally 

 varying both to rather normal syenite and almost to granite. No. 

 25 of the table represents a thin section of the rock. It contains 

 many very narrow highly quartzose bands parallel to its foliation. 

 On the northern slope of Roundtop mountain the grano-syenite 

 clearly grades into the granite. 



Quartz diorite facies of the syenite. The quartz diorite facies 

 of the syenite are most abundantly represented in the areas of the 

 southern part of the quadrangle. Thus much of the rock in the 

 large area in which are located Efner and Hunt lakes is medium- 

 grained, well-foliated quartz diorite. On the little hill just east of 

 Hunt lake there are good ledges of highly foliated quartz diorite 

 distinctly porphyritic in texture with phenocrysts of feldspar up to 

 an inch long scattered through a medium-grained matrix. No. 8 

 of the accompanying table represents a thin section of this rock. 

 Along the road for nearly a mile east of the area of mixed rocks 

 (see map) there are excellent exposures of highly foliated, some- 

 what porphyritic, apparently more or less sheared quartz diorite 

 varying almost to granite. A thin section of this quartz diorite is 

 represented by no. 10 of the table. The quartzes are highly flat- 

 tened and the scattering phenocrysts of feldspar are more or less 

 flattened to so-called " augen." Some lighter colored bands with 

 indefinite boundaries parallel to the foliation are notably more 

 acidic in composition. In the northeastern part of the area the rock 

 appears to be the more normal quartz syenite. North of Jenny lake 

 the rock is mostly highly foliated and moderately porphyritic, but 

 it is less quartzose than that farther east. South of the three lakes 



