44 



NEW YORK STATE MUSEUM 



absent or only sparingly present, ledges of such rock being very 

 difficult to distinguish from aj basic phase of syenite. Under the 

 microscope, however, the distinction may generally be made. 

 Where fresh the rock is greenish gray, and it weathers to brown. 

 The mineralogical compositions of selected samples of various 

 phases of the rock are shown in table 3. Labradorite and andesine 

 are always present, and oligoclase usually. Microperthite occurs 

 in most of the specimens in varying amounts up to 30 per cent, 

 and orthoclase in most specimens in varying amounts to over 50 

 per cent. A little quartz is generally present. All the thin sections 

 examined show greenish gray monoclinic pyroxene, sometimes 

 diallage. A little green hornblende nearly always occurs up to 14 

 per cent. Garnet varies from none to 12 per cent. Ilmenite (or 

 magnetite) up to a few per cent never fails. Apatite and pyrite 

 in small amounts always occur. N'. LI. Bowen, in a recent paper,^ 

 states that he has observed, in the transition rock from anorthosite 

 to syenite, inclusions of potash feldspar which are small patches, 

 uniformly oriented, and, in some cases, surrounded by areas of 

 plagioclase dififering from the crystal as a whole. A few slight 

 suggestions of this sort of thing were noted by the writer, but 

 certainly this is not a characteristic feature of the Keene gneiss 

 thin sections examined. 



Table 3 Thin sections of Keene gneiss 



d 



d 







a) 











M 

 



J! 

 



u 

 



C 



CD 





 







X) 



a 



4) 



c 



0) 



C 







a 



< 





 



Oh 



s 



G 

 



0) 



3 



10 



4f 8 

 7 f 7 a 

 14 g 4 

 14 b 4 

 16 j 7 

 I k 10 a 

 I k lob 



ol.-Lab. 80 

 ol.-Lab. 28 

 An. -Lab. 66 



ol.-An. 48 

 An.-Lab.30 

 An. -Lab. 70 



ol.-Lab. 40 



10 



25 



20 



20 

 32 



20 

 20 



51 

 10 



4 



2 

 9 

 5 

 I 



" '6 

 4 

 5 

 3 

 3 

 2 



3 



I 



2 



little 

 12 



I 



1 



little 

 little 



i 



1 



1 



little 



1 



little 

 i 



little 











11 



2 

 8 



8 



14 



5 



2 



6§ 









12 



41 

 42 

 45 



i 



I 

 I 



5 



'little 



1 



little 



little 



2 















No. 3, I mile east-northeast of Malcom p'ond; no, 10, i mile a little 

 south of west of High fall; no. 11, one-half of a mile south of the summit 

 of Catamount mountain; no. 12, one-half of a mile north of Franklin 

 Falls; no. 41, in the brook i34 miles due west of East Kilns; nos. 42 

 and 45, by the main road at northern edge of the village of Keene. 



1 Jour. Geol. 25 :22i. 1917. 



