Eggleston — Eruptive Rocks at Cutting sville, Vt. 381 



Strikes and dips of the country rocks are indicated 

 upon the accompanying map. The strikes are commonly 

 northeasterly, in accord with the usual Appalachian 

 trend and run at high angles to the axis of the 

 eruptive bodies. 



Structural relations among the members of the 

 country-rock series are obscure. The hornblendic 

 gneisses commonly strike at an angle to the other mem- 

 bers and are probably intrusive into them. The struc- 

 tural complexity makes it difficult to state the nature of 

 the rocks beneath those actually visible. Quartzite and 

 less certain dolomite xenoliths in the essexite of one of the 

 northern eruptive bodies may have been derived wholly 

 from beds formerly overlying the visible country rocks, 

 although some may have come from beneath. 



Whittle* refers the country rocks to the Algonkian and 

 places them in a system named by him the Mount Holly, 

 from a neighboring hill and village. 



Eruptive Rocks. 



The eruptive rocks include essexite, hornblende-biotite 

 syenite, pulaskite, nephelite syenite, sodalite-nephelite 

 syenite, nordmarkite, essexite porphyry, tinguaite, camp- 

 tonite, and an eruptive breccia. Some of the eruptives 

 have locally suffered slight faulting and possibly very 

 limited crushing and shearing along certain contacts, as a 

 result of successive intrusions and later movements ; but 

 all these rocks are entirely free from anything at all com- 

 parable to the effects of regional metamorphism dis- 

 played by the country rocks. 



Composite stock. — Cross-cutting relations to the 

 country rocks, combined with high outward dips of the 

 contact where observable, nearly vertical flow lines, and 

 small areal extent of the intrusive mass, indicate that 

 the main body is a stock. In any case a laccolithic origin 

 cannot be assumed. The composite character of the body 

 is revealed by the distribution and structural relations of 

 its rocks. The chief types are arranged in a roughly 

 concentric manner (see fig. 1), essexite being partly sur- 

 mounted by pulaskite and both being probably cut by the 

 nordmarkite body. 



* C. L. Whittle, The Occurrence of Algonkian Eocks in Vermont and the 

 Evidence for their Subdivision, Jour. Geology, vol. 2, p. 396, 1894. 



