180 GREEN MOUNTAINS IN MASSACHUSETTS. 



plates, magnetite, zircon, rutile, etc. (Thus at locality 616, in the gneiss 

 area west of King Cole mountain and Maple Grove station.) 



THE GREYLOCK SCHIST. 



This also consists of schists resembling in their petrographic character, 

 appearance, and structure those of the Berkshire schist formation. If there 

 be any difference between them it consists in that the upper schists are 

 more chloritic and albitic, and less frequently calcareous or plumbaginous 

 than the lower ones, but all the minerals occurring in the Berkshire schist 

 recur in the Greylock schist. 



The interleaved plates of ilmenite and chlorite are the same as in 

 the Berkshire schist, (Thus specimens from locality 1,076 in the most 

 southerly of the Hopper ravines, about 1,300 feet below Greylock summit.) 



The magnetite octahedra are also frequently met. (Thus at locality 

 449 in the cliffs on the south side of Saddle Ball, and again west of the 

 top of Grevlock about a quarter of a mile east of locality 1,076.) 



The feldspathic schists of this formation are characterized here and 

 there by large crystals of albite. At locality 709, on the west side of the 

 Notch, east of Mount Fitch near section F, the rock might be called an 

 albite-gneiss. It consists of "numerous squarish albite crystals, rarely in 

 simple twins, crowded closely together," but surrounded by "interlacing 

 fibers of museovite, chlorite, and biotite with magnetite grains and many 

 tourmaline needles. Quartz occurs rarely, in little grains or aggregates. 

 The biotite and chlorite are often in separate masses, but often pass into 

 one another in the same piece. Some of the chlorite may result from the 

 hydration of biotite. The feldspai - s contain inclusions of museovite, chlo- 

 rite, biotite, magnetite, tourmaline, etc." Mr. Wolff separated the feldspar 

 of this rock by the use of the Thoulet solution, and a double analysis of it 

 was made at the chemical laboratory of the U. S. Geological Survey in 

 Washington by Mr. R. B. Kiggs (F. W. Clarke, chief chemist). The result 

 shows the feldspar to be an almost pure albite. 



