Eggleston — Eruptive Rocks at Cutting sville, Vt. 393 



I n III IV v VI 



MgO 7-26 10-200 9-74 1-11 3-62 2-54 



CaO 12-42 12-807 12-60 10-24 9-68 10-52 



Na-0 3-21 3139 3-18 608 3-14 2-95 



K.,6 1-68 1-489 1-60 1-44 2-65 1-95 



H,0 (by ignition) 0-48 0-330 000 0-48 0-24 



F 0-31 



P 2 5 0-63 



Sum 100-92 99-762 10101 99-64 98-63 99-96 



I = Hornblende from Cuttingsville hornblende-biotite syenite, C. D. Test, 

 analyst. 

 II — Hornblende from Mt. Johnson, Quebec, essexite, F. D. Adams, Jour. 

 Geology, vol. 11, p. 260, 1903. 



III = Hornblende from Heum, Norway, heumite, J. P. Iddings, ' ' Eock 



Minerals," 1906, p. 338. 



IV = Barkevikite from Barkevik, Norway, nephelite syenite, ibid., p. 339. 

 V = Barkevikite from Barkevik, Norway, syenite, ibid., p. 339. 



VI = Barkevikitie hornblende from Square Butte, Mont., sodalite syenite, 

 L. V. Pirsson, U. S. Geol. Surv., Bull. 237, p. 67, 1905. 



Chemically, as well as optically, this Cuttingsville 

 amphibole is seen to be a barkevikitie hornblende. 



Chief among the remaining minerals, in thin sections 

 of the type phase of the Cuttingsville hornblende-biotite 

 syenite, is brown biotite which is present in amount 

 nearly equal to hornblende. There are occasional tri- 

 angular and irregular areas, filled with alteration prod- 

 ucts probably derived from nephelite, which is not 

 otherwise represented in the type phase of the syenite, 

 though visible to the naked eye in coarser-grained segre- 

 gations to be described hereafter. 



Apatite, titanite, magnetite, zircon, and pyrite are 

 accessory. 



The abundant plagioclase allies it to monzonite, but 

 the ratio of dark silicates to feldspar warrants the desig- 

 nation of the rock as a hornblende-biotite syenite. Its 

 analysis is given in the succeeding table (column I), 

 which introduces relevant analyses from similar rock 

 bodies and also the average analysis of laurvikite : 





I 



II 



III 



IV 



V 



VI 



VII 



SiO, 



57-44 



57-44 



59-96 



5901 



56-85 



57-12 



57-45 



TiO, 



0-69 



1-97 



0-66 



0-81 









AL'O s 



21-60 



19-43 



19-12 



18-18 



2156 



21-69 



2111 



Fe 2 O c 



0-20 



1-69 



1-85 



1-63 



3-44 



1-63 



2-89 



FeO 



2-62 



2-70 



1-73 



3-65 



1-14 



3-65 



2-39 



MnO 



0-14 



0-25 



0-49 



003 









MgO 



1-09 



1-16 



0-65 



1-05 



0-85 



1-55 



106 



CaO 



2-90 



2-66 



2-24 



2-40 



5*26 



403 



4-10 



Na,0 



7-36 



6-48 



6-98 



7-03 



607 



5-93 



5-89 



K 2 



412 



4-28 



4-91 



5 34 



3-66 



3-48 



3-87 



