PETROGRAPHIC PROVINCE OF NEPONSET VALLEY, MASS. 157 



Pyroxene is represented only by a violet gray augite occurring in considerable 

 areas, always allotriomorphic and showing less altera ion than the feldspar does. 

 Iron oxide is present in the form of titaniferous magnetite and of ilmenite both 

 of which are abundantly altered to leucoxene, an alteration making more marked 

 the cubic cleavage of the former mineral and the rhombohedral cleavage of the 

 latter mineral which displays curiously branching forms. Apatite is abundant 

 as is usual in this type of rock ; olivine, biotite, and original hornblende are none 



of them present. The secondary constituents 



uralite, actinolite, chlorite 



epidote, albite, calcite, quartz, leucoxene, and pyrite; the first three are alteration 

 products of the pyroxene; epidote in minute, stoutly columnar crystals, scanty 

 albite, quartz, chlorite, and calcite are alteration products of the feldspar. 



Neponset Valley Igneous Rocks. 



i. 



Normal Granite 



71.34 

 13.97 

 1.95 

 1.00 

 0.62 

 1.63 

 4.83 

 3.89 

 0.80 

 0.09 



0.43 

 trace 



100.55 



II. 



Batholith. 



Fine-grained 

 Granite. 



76.52 



12.30 

 0.70 

 0.56 

 0.16 

 0.31 

 5.19 

 4.58 

 0.41 

 0.11 



none 

 0.12 



trace 



100.96 



III. 



IV. 



Arid Volcanic* 



Rhyolitic Faries. 



71.63 



13.71 



2.09 



1.76 



0.19 



1.31 



3.24 



4.49 



0.51 



0.08 



0.41 



0.34 



trace 



trace 



trace 



99.76 



Aporhyolile Lava. 



72.85 

 12.92 



2.98 



0.38 

 0.90 

 7.08 

 3.01 



0.65 



100.77 



v. 



vi. 



Acid Volcanics. 



(Center) Dike 

 73.72 



13.22 



1.48 



1.72 



0.66 



0.65 



4.52 



2.90 



0.36 



0.10 



0.15 



0.34 

 trace 



(Border) Dike. 



99.82 



71.73 

 15.00 

 1.54 

 1.05 

 0.86 

 0.69 

 4.69 

 2.90 

 0.94 

 0.14 



0.19 



0.35 



trace 



100.08 



VII. 



VIII. 



Trachyte. 



65.41 



16.09 

 3.84 

 0.95 

 1.51 

 2.93 

 6.54 



0.57 

 1.06 

 0.13 

 0.47 

 0.51 

 trace 



trace 



Intermediate. 



IX. 



X. 



Basic Volcanic*. 



Acid Andesite Dike. I Andeaite Lava. 



62.80 

 19.84 



8.70 



Relatively low in 



CaO and high in 

 MgO 



53.75 



18.37 



8.28 



5.63 

 3.22 



7.05 

 1.20 



3.34 



Andesite Dike 



45.30 



16.07 

 8.26 

 2.17 



5.58 

 5.63 

 2.44 

 4.06 

 2.93 

 0.30 

 4.78 

 1.70 

 0.20 

 0.43 



100.01 



100.84 



99.85 



• • 







