70 



ROCKS FORMED THROUGH IGNEOUS AGENCIES 



Chemical Composition of Syenite 



CONSTITITBNTS 



Silica (Si02) . . , 

 Alumina (AI2O3) . 

 Ferric iron (Fe203) 

 Ferrous iron (FeO) 

 Magnesia (MgO) . 

 Lime (CaO) . . . 

 Soda (NagO) . . , 

 Potash (K2O) . . 

 Ignition (H2O) . . 

 Ciilorine (CI.) . . 



} 



60.02% 

 16.66 



7.21 



2.51 

 3.59 

 2.41 

 6.50 

 1.10 



100.00 % 



II 



{ 



57.37% 

 13.84 



2.44 



3.44 



6.05 



5.53 



1.53 



4.47 



97.84 % 



in 



54.15% 

 18.92 



.6.79 



1.90 

 3.72 

 5.47 

 8.44 



0.42 



99.81 



IV 



63.45% 

 18.31 

 ■ 0.42 

 . 3.56 



0.35 



2 93 



0.06 



5.19 



0.30 



99.57% 



geological nomenclature by Voltz in 1828 (Teall), is applied 

 to a fine-grained mica orthoclase rock, ocenrring only in the 

 form of dikes and further differing from the typical syenites in 

 having a porphyritie rather than granitic structure. Vogesite 

 is the name applied to a similar rock in which hornblende or 

 augite prevails in place of mica. These rocks are placed by 

 Professor Rosenbusch in his latest work in the group of syenitic 

 lamprophyrs. MonzoniU is a varietal name for the augite syenite 

 of Monzoni in the Tyrol. 



The mode of occurrence of the syenites is similar to that 

 of the granites, though they are much more limited in their 

 distribution. In the United States they have thus far been 

 described but sparingly. Marblehead Neck, Massachusetts; 

 Jackson, New Hampshire, are well-known localities; a beauti- 

 ful hornblende syenite is found among the glacial drift boulders 

 about Portland, Maine, but its exact source is not known. The 

 hornblende syenite described by Hawes as occurring at Red 

 Hill, Moultonborough, New Hampshire, has been shown by 

 Professor W. S, Bayley^ to carry eteolite, and to belong to the 

 group of elcfiolite syenites. Hornblende syenites occur in the 

 Vosges Mountains of Germany and in Saxony; mica syenites 

 or minettes in the Odenwald, Germany, Baden, Saxony, and in 

 the Fichtelgebirge. A mica-augite syenite carrying sodalite 

 occurs as a Cretaceous eruptive in Jefferson County, Montana,^ 



^Bull. Geol. Soc. of America, Vol. Ill, 1892. 

 ^rroc. U. S. Nat. Museum, Yol. XVII, 1894 



