Eggleston — Eruptive Rocks at Cutting sville, Vt. 407 



main eruptive body is a composite stock. It is certainly 

 not a laccolith and probably not a chonolith. The two 

 small eruptive areas north of the main body seem to be 

 parts of a single, small, satellitic stock or chonolith, if 

 not simply a northward prolongation of the main body, 

 now separated in outcrop by fluviatile and glacial 

 deposits. 



Comparison with other areas. — The general structure 

 is comparable to that of Ascutney Mountain, not more 

 than 25 miles distant, which is also a composite stock. 

 There biotite granite and diorite appear in addition to 

 types which almost duplicate certain of the Cuttings- 

 ville rocks. 



Though the main Cuttingsville body has a rough con- 

 centric structure, its relations to country rock recall those 

 of at least four stocks of the Monteregian Hills, Quebec, 

 namely, St. Hilaire, Rougemont, Johnson (a neck?), and 

 Yamaska Mountains. Of the other Monteregian masses, 

 Shefford, Brome, and St. Bruno (Montarville) are com- 

 posite and have been described as laccoliths, without 

 compelling evidence. 



In all of these hills, essexite is represented. In sis 

 (perhaps all) of them the essexite is associated with 

 syenite. This association, combined with close mineral- 

 ogical and chemical similarity to the Ascutney and Cut- 

 tingsville eruptives, renders the comparison doubly 

 impressive. 



Red Hill, N. H., a neighboring New England locality, 

 furnishes another example of a small, composite syenite 

 stock, described by Pirsson. 4 The country rock is a 

 granitic gneiss, and the eruptives include, in the order of 

 eruption, nephelite syenite (umptekite, foyaite), aplite, 

 paisanite, bostonite, syenite porphyry, and camptonite. 

 Chemical similarity of the Red Hill umptekite and the 

 Cuttingsville, Vt., hornblende-biotite syenite has been 

 noted. 



Essex county, Mass., the type locality for essexite, and 

 Southboro, Mass, a tinguaite locality, are other examples 

 of New England areas containing eruptives chemically 

 related to certain of the Cuttingsville rocks. 



The Cuttingsville area thus takes its place as one more 

 of the known number of small alkaline intrusive bodies 

 in the New England-Quebec region. Most of the Monte- 



* L. V. Pirsson," this Journal, vol. 23, p. 257, 1907. 



