TRANSITION ROCKS 443 



Along the main brook, for one-fourth of a mile after it enters the area, 

 there are good exposures of homogeneous, scarcely gneissoid Keene gneiss, 

 with phenocrysts not as large as usual. This rock, whose composition is 

 given as number 41 of the above table, has strong syenite affinities because 

 of its high orthoclase content. In this portion of the area syenite magma 

 quite certainly completely assimilated more or less anorthosite. 



At one place on the little hill, in the eastern part of the area, fairly 

 coarse granite is intimately associated with gabbroid Whiteface anortho- 

 site with local development of what appears to be an assimilation product 

 containing some quartz. 



SOME OCCURRENCES IN THE SCHROON LAKE QUADRANGLE 



An outcrop on the southern brow of Cobble Hill, 1 mile due south of 

 Bailey Pond, is very significant because of the light it throws on the local 

 origin of the Keene gneiss. The accompanying sketch (figure 2) shows 

 the relationships. This Keene gneiss is distinctly granitic in appearance 

 except for the many labradorite crystals, mostly about an inch long, which 

 stand out as distinct phenocrysts more or less parallel to the crude folia- 

 tion of the otherwise medium grained rock. Within this rock are inclu- 

 sions of Whiteface anorthosite, which . contains some large labradorites 

 and also scattering femic minerals up to two inches long, more or less 

 lenslike and parallel to a distinct foliation. Contacts between the inclu- 

 sions and the Keene gneiss are not very sharp. Immediately above this 

 Keene gneiss, but not in very sharp contact with it, is a very gneissoid 

 granitic gneiss which contains many garnets. This granitic gneiss grades 

 upward into typical, medium grained, only moderately foliated granite 

 without garnets. A similar typical granite lies against the Keene gneiss 

 at the bottom, but the contact there is quite sharp. My interpretation is 

 that the upward moving granite magma more or less assimilated some 

 Marcy anorthosite at a considerable depth, and that this molten mass 

 (Keene gneiss magma) having risen still higher caught up and only 

 fused the borders of fragments of Whiteface anorthosite. The origin of 

 the garnetiferous granite is not so certain, though it may represent a mass 

 of granite with a small quantity of anorthosite very thoroughly digested. 



Interesting exposures occur in a small area near the southeastern base 

 of Severance Hill. The rocks are mostly peculiar basic-looking syenitic 

 gneisses, well foliated, medium to fine grained, garnetiferous, and green- 

 ish gray where fresh, but they are quite variable with considerable local 

 development of quartz. They differ from the typical Keene gneiss in not 

 having the large bluish labradorites. I hav« not yet had opportunity to 

 study thin sections of this rock. One large exposure shows numerous 



