Eggleston — Eruptive Rocks at Cutting sville, Vt. 401 



in narrow dikelets and streamers cutting the type and 

 coarser phases. 



Green hornblende, with accessory quartz, is notable in 

 certain thin sections. Part of the hornblende is prob- 

 ably secondary. The presence of hornblende and quartz 

 allies this phase to the Ascutney Mountain nordmarkite, 

 and less closely to the Shefford Mountain nordmarkite. 



Near the summit of the south knob of Granite Hill a 

 porphyritic syenite, tentatively mapped as nordmarkite 

 (5, fig. 1), is closely associated with essexite not far from 

 the country-rock contact. Apparently it is a border 

 development of the eruptive body, and of small extent. 



In the zone between nordmarkite and essexite, on the 

 upper north slope of the north knob of Granite Hill, the 

 nordmarkite becomes increasingly biotitic. Some of it 

 also carries roughly idiomorphic hornblende and plagio- 

 clase, which are sometimes arranged in flow lines. The 

 rock grades from medium-grained to fairly fine, and from 

 granitic to porphyritic. It becomes so much, like the 

 adjoining essexite that the actual contact is somewhat 

 indistinct. The contact rock is perhaps best classified as 

 an essexite-nordmarkite hybrid. 



Dike Rooks. 



Essexite porphyry. — The apophyses from the essexite 

 are generally porphyritic. Petrographically this essex- 

 ite porphyry has no special peculiarities worthy of 

 detailed statement. Hornblende and biotite, alone or 

 together, are the chief phenocrysts. 



Nephelite syenite. — As already noted, nephelite syenite 

 forms dike-like bodies in the hornblende-biotite syenite 

 of the quarry (Q 2, fig. 1). 



Syenite porphyry. — Pulaskite porphyry and nord- 

 markite porphyry are developed at the borders of both 

 the pulaskite and nordmarkite masses. An account of 

 porphyritic phases of pulaskite and nordmarkite has been 

 given. These phases pass into pulaskite porphyry and 

 nordmarkite porphyry, at contacts and in apophyses, by 

 increase of groundmass. 



Some of the pulaskite porphyry is apophysal from the 

 main pulaskite body, but other masses form dikes which 

 seem to be distinctly later intrusions. Two or more of 



Am. Joue. Sci— Fourth Series, Vol. XLV, No. 269.— May, 1918. 



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