B. K. Emerson — Northfieldite. 215 



the other is perfectly exposed. It is a fine-grained light- 

 colored rock, sometimes quite biolitic and garnet, zircon, 

 rutile and a little feldspar are found in it with the microscope. 



The rock in this western area generally contains many 

 minute needles of tremolite or actinolite, but this may be 

 assumed to be from absorption from a former cover which in- 

 cluded the thick Bernardston limestone since it is wanting in 

 the eastern occurrences, and since calcite is also found in the 

 neighboring granite in many places. Indeed, two miles north 

 of Mt. Orient a small enclosure of coarse crystalline limestone 

 was fonnd in the northfieldite, and on the contact the latter 

 rock contains much more and coarser actinolite than a few 

 inches away. 



At South Leverett mill, south of "West Pelham and else- 

 where, the actinolite is abundant also in the common gneiss 

 adjacent to the Northfieldite and so is not characteristic of the 

 northfieldite but is derived by both rocks from the limestone 

 which seems to have extended from the Bernardston bed on 

 the north to the limestone bed in Belchertown on the south. 



Analyses of northfieldite. 



12 3 



SiO,. 93-38 93-20 83-04 



A1,0 3 3-09 2-86 6-92 



Fe„0. 



FeD -72 -79 1-34 



■ }... 



Ti0 2 - -12 -12 -12 



CaO -34 -68 3-20 



MgO -43 -27 1-98 



Na 2 -50 not det. not det. 



K,0 1-32 



P.O. none none -04 



80-63 



6-22 



1-59 



•21 



3-69 



3-27 



not det 



•02 



99-90 97-92 96-64 95*63 



1. Northfieldite, Mt. Orient, Pelham, average rock, trace of 

 actinolite. E. T. Allen, analyst. 



2. Northfieldite, 60 feet below summit on the west slope and so 

 about 60 feet above trace of biotite. E. T. Allen, analyst. 



3. Coarse actinolite-biotite northfieldite. Hollow at east foot 

 of Mt. Orient. In the gneiss. E. T. Allen, analyst. 



4. Highly actinolitic northfieldite. Mt. Orient, south face 2-3 

 feet above base. This contains minute flakes of graphite. It was 

 carefully tested for molybdenum without success by Mr. Allen. 



5. Northfieldite, 2 inches from calcite. 2 miles NE. of Mt. 

 Orient. John B. Zinn, analyst. 



