382 Eggleston — Eruptive Rocks at Cutting sville, Vt. 



Essexite composes nearly one-quarter of the total area 

 of the eruptives. In practically all of its occurrences it 

 is cut by syenite or syenite porphyry, the smaller masses 

 apparently being completely inclosed. Evidently the 

 essexite represents an older body, probably a stock, which 

 has been invaded and largely engulfed by the later intru- 

 sions. Nearly vertical contacts and occasional nearly 

 vertical flow lines, in the essexite and some of the sye- 

 nite, suggest that the whole forms a composite stock. > 



Fig. 3. 



Fig. 3. Granite Hill, looking southwest. 



The pulaskite, especially well shown on the north 

 slopes of the bowl, constitutes about two-thirds of the 

 main eruptive body. It clearly penetrates the essexite 

 and gneisses. In places it extends west of the crest of 

 the middle part of Granite Hill (fig. 3), forming, where 

 essexite is present, a band of no great width between the 

 essexite and gneisses. 



Between flanking lenses of essexite and occupying the 

 crest of the middle part of Granite Hill, is an area of 

 Jiomblende-biotite syenite, upwards of 1,000 feet long and 

 half as wide. It appears again, in a much narrower 

 band, near the crest of the north knob. Its total areal 

 extent is believed to be least of all the chief types of rock 

 exposed on Granite Hill. Its structural relations to both 

 the essexite and the pulaskite are somewhat obscure, due 

 to the failure of sharp contacts. A point bearing upon 

 this question, however, is the very common development 

 of a biotite-hornblende phase of the pulaskite on the side 

 towards the essexite. These border phases frequently 



