PROCEEDINGS OF THE NATIONAL MUSEUM 

 Table of norms 



VOL. 71 



I. Quartz monzonite. West Brush Creek, Crested Butte quadrangle, Colo. Nearly identical with the 

 mass in the Sawtooth Range. Washington's Tables, p. 374. 



II. Quartz monzonite. From a large asymmetrical laccolith, Mount Marcellina, Anthracite qnad- 

 rangle, Colo. Washington's Tables, p. 254. 



III. Quartz monzonite porphyry. Storm Ridge. Anthracite quadrangle, Colo. Washington's Tables, 

 p. 246. 



IV. Quartz monzonite. Sultan Mountain, near Silverton, San Juan region, Colo. Washington's Ta- 

 bles, p. 246. 



V. Quartz monzonite. Electric Peak, Yellowstone National Park. Washington's Tables, p. 254. 



VI. Quartz monzonite. Frisco district, Utah. Washington's Tables, p. 374. 



VII. Quartz monzonite, near Pinal Peak, Globe district, Arizona. Washington's Tables, p. 376. 



VIII. Quartz monzonite porphyry. Grass Valley, Nevada County, Calif. Washington's Tables, p. 382. 



The intrusive mass wliich extends from North Italian Mountain 

 to the summit of Italian Peak proper is very much like the J5ne- 

 grained quartz monzonite of which a description and analysis have 

 been given. It is, however, more variable in texture and composi- 

 tion than the larger body. The common facies is a qiiartz-biotite- 

 hornblende rock, but augite appears in some places, and near the 

 contacts hornblende is apt to be more abundant than elsewhere. A 

 crude prophyritic texture appears here and there, though a develop- 

 ment of orthoclase in a few phenocrysts 1 to 2 cm. in diameter and 

 locally plagioclase and hornblende are conspicuous. 



The rock of South Italian Mountain differs but little in any essen- 

 tial respect from that of the northern summit. It is the older 

 intrusive and, due to incipient alteration of the orthoclase by dis- 

 semination of ferric hydroxide particles all through most grains, 

 there is a dull pinkish tinge to this feldspar, causing the appearance 

 of more potash feldspar than is actually present. The same impreg- 

 nation is also exhibited to a lesser extent in the plagioclase. Reex- 

 amination of this rock makes it probable that the plagioclase (oligo- 

 clase-andesine) is probably as abundant as orthoclase, if not more so, 

 and the name quartz-monzonite applies to that rock of both intrusives. 



