Eggleston — Eruptive Rocks at Cutting sville, Vt. 385 



breccia is intimately injected by a trappean rock, possi- 

 bly an essexite porphyry. The exposures indicate an 

 elongate mass, about half a mile long and 500 feet wide, 

 lying en axe with the eruptive bodies. The eruptive 

 rocks of the small areas farther south are bordered by, 

 and alternate with, brecciated country rock. All the 

 breccias may form a single band, the most northerly mass 

 being not so much injected by igneous rock because of 

 greater distance from the eruptive center. 



Fig. 4. 



Fig. 4. Area of breccia, two miles northwest of Cuttingsville. Standard 

 orientation. Scale, 1 : 21,000. Area shown is nearly continuous with that of 

 figure 1. B, breccia. L, limestone. Other rocks not distinguished. 



Dikes. — Associated with the plutonic rocks are numer- 

 ous dikes, both aschistic and diaschistic. They comprise, 

 in the inferred order of intrusion, essexite porphyry, 

 nephelite syenite, syenite porphyry, aplite tinguaite, and 

 camptonite. 



As a whole the dikes have not been thoroughly diag- 

 nosed. Two, a syenite-porphyry dike and a tinguaite 

 dike, mapped respectively at T and D, fig. 1, have been 

 chemically studied. Classification of the other dikes is 

 tentative. Some mapped as tinguaite may, upon fur- 

 ther study, prove to be fine-textured phases of syenite 

 porphyry, or possibly bostonite. Others mapped as 



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



27 



