158 PETROGRAPHIC PROVINCE OF NEPONSET VALLEY, MASS. 



The system, trending north and south, includes dikes up to fifteen feet in width, 

 the most recent igneous rocks of the province, basaltic in character, and char- 

 acterized by a marked spheroidal weathering with the separation of successive 

 rusty yellow oxidized coats. A specimen from one of the largest of these dikes 

 exposed on Stimson Street shows considerable green hornblende and a finely 

 diabasic structure. 



Norms. 

 Batholith. 



Granite. 



Quartz 



Orthoclase . . 

 Albite.. ... 

 Anorthite. . 

 Wollastonite 

 Enstatite . . . 

 Magnetite. . 

 Ilmenite . . . 



Hematite . . . 

 Water 



I. 





24.72 

 22.80 

 40.87 

 5.00 

 1.28 

 1.60 

 2.09 

 0.76 

 0.48 

 0.89 



Microgranite. 



Quartz 



Orthoclase 



Albite 



ivcnut6 ...... •*. 



Sodium metasilicate 



Diopside 



Hypersthene 



Ilmenite 



Water 



II 



Rhyolite. 



30.48 

 27.24 

 37.73 

 1.85 

 0.98 

 1.43 

 0.60 



0.15 



.52 



100.58 



Quartz 



Orthoclase . . 

 Albite..... 

 Anorthite . . . 

 Corundum. . 

 Hypersthene 

 Magnetite. . 

 Ilmenite 



Water 



C0 2 



III. 



32.16 

 26.69 

 27.25 

 6.39 

 1.12 

 1.42 

 3.02 

 0.61 



0.59 

 .41 



99.66 



Norms. 



Neponset Valley Volcanics. Acid Volcanics 



Quartz 



Orthoclase. . 



Albite 



Acmite 



Wollastonite 

 Enstatite . . . 



Water 



Effusive 



Aporhyo- 



lite IV. 



Intrusives. 



21.00 



17.79 



49.78 



8.78 



1.86 



1.00 



0.65 



100.16 



Quartz 



Orthoclase. . 



Albite 



Anorthite . . . 

 Corundum. . 



Hypersthene 

 Magnetite. . 

 Ilmenite 



Water 



CO, 



33.18 

 17.24 

 38.25 

 3.34 

 1.43 

 3.15 

 2.09 

 0.61 

 0.46 

 0.15 



99.90 



I. Grano-lassenose (Class 1, order 4, rang 2, subrang 4). 



II. Grani : liparose (Class 1, order 4, rang 1, subrang 3). 



III. Phyri-toscanose (Class 1, order 4, rang 2, subrang 3). 



Jr _£ n yri- kallerudos e (Class 1, order 4, rang 1, subrang 4). 

 V. Phyn-kallerudose (Class 1, order 4. ran? 1 snhr«™ dV 



VI. 



kallerudose 



Quartz 



Orthoclase . . 



Albite. 



Anorthite . . . 

 Corundum. . 

 Hypersthene 



Magnetite . . 

 Ilmenite 



Water 



C0 2 



17.24 



39.82 

 3.34 

 2.86 

 2.33 

 2.32 



0.61 

 1.08 



319 



100H 



Zlh p jbyn-manposose (Class 1, order 4, rang 2, subrang 5). 

 r-i ^ Ophiti-neponsetose (Class 2, order 6, rang 2, subrang 5). 

 IX. Ortnpnyn-shoshonose (Class 2, order 5, rang 3, subrang 3). 



No analysis was made of the diabase of this district ; presumably it offers 

 nothing of peculiar interest. 



