PETROGRAPHIC PROVINCE OF NEPONSET VALLEY, MASS. 145 



Norms. 



Quartz 



Orthoclase . 



Albite. 



Anorthite . . . 

 Diopside. . . 

 Hypersthene 

 Magnetite. . 



28.9 

 6.7 



58.2 

 1.7 

 2.6 

 0.5 



Acmite .... 

 Wollastonite 

 Enstatite . . . 



II.a. 



|III.a.w 



21.00 



20.3 



17.79 



23.4 



49.78 



45.1 



8.78 



7.4 



1.86 





1.00 



3.0 





0.5 



Anorthite . 

 Corundum 



iV.a. 18 



22.8 

 30.6 

 40.3 

 0.6 

 1.1 

 1.4 

 2.4 



Ilmenite. 

 Hematite 



V.a.» 



23.3 

 21.1 



44.0 



6.1 



0.6 



1.3 

 0.7 



1.7 

 1.3 



I.a. Noyangose (Class 1, order 4, rang 1, subrang 5). 



II.a. Phyri-kallerudose (Class 1, order 4, rang 1, subrang 4). 



Ill.a. Grano-kallerudose (Class 1, order 4, rang 1, subrang 4). 



IV.a. Liparose (Class 1, order 4, rang 1, subrang 3). 



V.a. Lassenose (Class 1, order 4, rang 2, subrang 4). 



The rhyolites, aporhyolite, keratophyre, and soda-granite are alike in class 

 and order, and with the exception of the Marblehead Neck rhyolite, which has 

 a relatively larger percentage of lime, are alike in rang but differ slightly in the 

 relation of the molecular weights of the alkalies. The keratophyre is sodi- 

 potassic, the aporhyolite, soda-granite, and the Marblehead Neck rhyolite arc 

 dosodic and the California rhyolite persodic. 



Aporhyolite Pyroclastics . — Fragmental volcanics are exposed near the crossing 

 of Blue Hill Avenue by the New England Railroad; they are well displayed in 

 ledges north of the railroad, on Blue Hill Avenue south of Brook Street, Milton; 

 near Harvard Street and Mount Hope Cemetery; in a quarry near Mount Cal- 

 vary cemetery, on Rutledge Road, Rugby, at the intersection of River Street 

 and the New England Railroad, and south of Norfolk Street and the New England 

 Railroad. Rhyolitic tuff and breccias are also well displayed in the district 

 included between Grove and Washington Streets, West Roxbury, on Bold Knob, 

 Stony Brook Reservation, and in Grew's wood. This tufaceous material varies 

 from a fine-grained consolidated ash to a breccia composed of fragments one to 

 two inches in diameter. In two cases the "aschen structur" which has been 

 described by Mugge 18 is a feature of the tufaceous volcanic. 



The forms which make up that texture appear only in ordinary light, and are 

 obscured or completely lost with crossed nicols on account of an extremely fine 

 quartz-feldspar mosaic which replaces the original fragmental and glassy texture 



of the lava. 



Where the recrystallization of fragments and matrix is not uniform, 



as is the case with the tufaceous material from Mount Calvary cemetery, the true 

 character of the rock is obscured but not obliterated in polarized light. A large 

 boulder of a blood-red color, found in the woods near Blue Hill Avenue, Milton, 



14 H. S. Washington, Professional Paper No. 14, U. S. Geol. Survey, 1903, p. 157. 

 ■ Op. cit., p. 155. 



* Op. cit., p. 145. 



* Op. cit., p. 173. 



u O. Mugge, " Untersuchungen iiber die Lenniporphyre in Westfalen und der angrenzenden 

 Gebieten," Neues Jahrbuch. f. Min. Geol. u. Pal., B. B. viii. 1893. 



10 JOURN. ACAD. NAT. SCI PHILA., VOL. XV. 







