Eggleston — Eruptive Rocks at Cutting 'sville, Vt. 395 



proportion of feldspar, much of which is plagioclase, 

 diminishes, the rock becomes dark-colored and gabbroid, 

 and grades into coarse-grained essexite. 



A strongly biotitic phase of medium grain, and with a 

 somewhat greater proportion of dark silicates than in the 

 type phase, is exposed along the railroad in the first 

 small eruptive area north of the Granite Hill area (fig. 1). 



In the hornblende-biotite syenite of the quarry on 

 Granite Hill (Q 2, fig. 1), foyaitic schliers are not 

 uncommon. Some appear to be segregations. Others 

 are more sharply defined, elongate, and dike-like. They 

 are usually small, but may attain a width of several 

 inches and a length of 2 or 3 feet. The larger are coarse- 

 grained, with gray nephelite, sometimes an inch or more 

 in diameter, white or pearl-gray feldspars, and an occa- 

 sional biotite flake or hornblende prism. Thin sections of 

 these schliers show microperthite, some plagioclase, 

 nephelite, colorless sodalite, hornblende, titanite, and 

 magnetite. In the finer-grained rock there also appear 

 olive-brown biotite, pyrite, and possibly cancrinite and 

 zircon as subordinate accessories. 



Pulaskite (3, fig. 1). — This rock is usually coarse- 

 grained and much weathered. The type phase is essen- 

 tially a coarse-grained aggregate of hypidiomorphic, 

 gray-white feldspars, which weather cream-white, yel- 

 lowish, or brownish. Biotite is generally present, 

 becoming abundant in some varieties. 



A thin section of comparatively fresh rock from the 

 exposure along Mill River at the east foot of the south 

 knob of Granite Hill shows the rock to be composed 

 chiefly of microperthitic feldspar with a little orthoclase. 

 One area probably represents cancrinite derived from 

 original nephelite. A little nephelite is almost certainly 

 present in some other hand specimens. Titanite, magne- 

 tite, pyrrhotite, apatite, and zircon are accessory; the 

 sulphides and titanite are sometimes macroscopically 

 visible. 



Some of the weathered rock from the upper southward 

 slope of the north knob of Granite Hill appears to carry 

 a little augite, as well as some biotite. If so, it 

 approaches augite syenite in composition, but is decidedly 

 more feldspathic and coarser-grained than the typical 

 augite syenite or nordmarkite (5, fig. 1) of the northward 

 slope of the north knob. It has been a difficult matter to 



