Eggleston — Eruptive Rocks at Cutting 'sville, Vt. 383 



resemble very closely the type hornblende-biotite syenite 

 in the quarry near the crest of the middle part of 

 Granite Hill. 



These facts might be explained on the assumption that 

 the hornblende-biotite syenite is a sort of hybrid, having 

 resulted from the assimilation of essexite by pulaskite. 

 This view accords with the usual absence of sharp con- 

 tacts between pulaskite and essexite, the one gradually 

 passing into the other, as illustrated in a narrow band 

 near the crest of the north knob. 



However, in the quarry the hornblende-biotite syenite 

 itself is cut by an apophysis or irregular dike of syenite 

 porphyry merging into porphyritic syenite. If it is a 

 tongue from the main mass of pulaskite, the view that 

 the hornblende-syenite is a hybrid of essexite and pulas- 

 kite must be relinquished in favor of early differentiation 

 and intrusion coincidently with or immediately succeed- 

 ing the essexite, but preceding the pulaskite. 



The nordmarkite is clearly intrusive into the essexite, 

 cutting it freely and inclosing fragments, as well shown in 

 the contact zone of essexite and nordmarkite on the north 

 knob. Its relations to the other syenites are obscure. 

 On the lower southeast slope of the north knob, the path 

 to the quarry has been cut in bedrock which shows quartz- 

 syenite dikes penetrating a pulaskitic type. 



A similar combination, with gneiss fragments also 

 included, is shown in excavated blocks at the edge of Mill 

 River just below. This is the only recorded evidence 

 that nordmarkite intrudes eruptives other than essexite, 

 and it is not conclusive. The nordmarkite along Mill 

 River, at the east foot of the north knob of Granite Hill, 

 is cut by several large dikes of syenite porphyry. 



These may possibly be apophyses from the pulaskite, 

 though there are certain field, lithological, and chemical 

 reasons for believing these syenite-porphyry dikes to be 

 intrusions later than both nordmarkite and pulaskite, 

 and connected with the nephelite syenite. 



The sodalite-nephelite syenite in the railroad cut is 

 probably considerably less extensive than any type on 

 Granite Hill. Very similar rock exposed on the lower 

 east slope of the south knob, in a small detached outcrop, 

 on the west shore of Mill River, may indicate that the 

 area extends into Granite Hill. The structural relations 

 are completely hidden. The rock is either a sodalite- 



