26 NEW YORK STATE MUSEUM 



netite and apatite. A tiny veinlet of quartz with a little calcite and 

 a kaolinized selvage runs across the slide. The rock is roughly 50 

 per cent microperthite, and 24 per cent each garnet and augite ; 

 the others making up the remainder. It is probably a crushed 

 member of the syenite series rather than an old Grenville gneiss. 

 The next slide contains the same minerals with the addition of 

 plagioclase, one crystal of the latter forming 10 per cent of the 

 slide. The last slide shows no microperthhe or augite, but is 

 plagioclase of medium acidity and hornblende. This variation is 

 within the limits of known changes in the syenitic rocks, and does 

 not preclude the originals from being intrusive syenite of variable 

 character. A short distance to the south of the mine another 

 exposure of gneiss like the middle one described above was observed. 

 The gneiss is succeeded by 25 feet of ophicalcite, and this by 

 15 feet of gneiss, which resembles green syenite. Nearly 50 feet 

 was then concealed, followed by a gneissoid rock, from which a 

 specimen on microscopic examination revealed an intimate inter- 

 growth of golden brown garnet and bright green pyroxene. It 

 is obviously a garnet contact zone and was probably once limestone. 

 While generally in rounded or irregular polygonal intergrowths, 

 there are some fingerlike interpenetrations. This rock continues 

 for 200 feet or more and was eventually succeeded by ophicalcite 

 or pyroxenic limestone containing the ore. Of the immediate asso- 

 ciates of the ore one could only judge from the dump. Obviously 

 garnets, pyroxene and calcite were mixed with it. For one-fourth 

 of a mile farther to the westward in the bed of the brook green, 

 syenitic gneiss, richly charged Vv^ith garnets can be traced in occa- 

 sional ledges. The huge boulders concentrated by the brook from 

 the very heavy moraine which fills the valley then make up the 

 bed for one-half of a mile or more. The brook is down in a gulch 

 in glacial drift estimated at 150 feet in vertical depth, and the 

 boulders range up to 15 or 20 feet in diameter. They are all 

 anorthosite. Ultimately the brook takes its rise in the anorthosite 

 of Cascade and Porter mountains. The nature of the green syenitic 

 gneiss is obscure. It may be intrusive syenite, but if so is extra- 

 ordinarily rich in garnet, a fact which might be explained by the 

 absorption of Grenville calcareous sediments. The gneiss may 

 belong to the Grenville, an interpretation which would seem to be 

 favored by the association of the limestone. The abundant garnets 

 might then be referred to the metamorphism of calcareous, sedi- 

 mentary admixtures. The former interpretation is here given 



