W. G. Foye— Nephelite Syenites of Ontario. 417 



Microscopic description. — The red syenite resembles very 



closely the rock described by Adams and Barlow* as umptek- 



ite. A rough estimate of the mineral composition of the 

 rock is : 



Orthoclase ._ 20 per cent. 



Microcline 10 



Albite .' 20 



Microcline-albite microperthite . 33 



Biotite 12 



Hornblende 0'15 



Calcite 4- 



Zircon . . "25 



100-00 



The biotite is olive-green in color. 



The hornblende is also olive-green and extinguishes at a 

 small angle. 



The albite has the approximate composition Ab 9 An,. 

 Calcite is present as irregular grains of primary origin. 

 The rock has an allotriomorphic granular texture. 



2. Schistose Canadite. 



Macroscopic description. — The tj'pical nephelite syenite of 

 the Haliburton area, of which this rock is an example, has 

 been called by Quensel,f canadite. It is distinguished from 

 the usual nephelite syenite by the predominance of albite 

 instead of a potash feldspar. It is a light gray rock, occasion- 

 ally dotted with pink. It is medium and even-grained. 



Biotite and feldspar are about equal in amount and form 

 the larger portion of the rock. The gray platy feldspar is 

 sometimes replaced by a pink variety. The rock breaks with 

 an irregular fracture and appears quite fresh to the unaided 



Microscopic description.— A thin section of this rock shows 

 that it is composed of calcite, biotite, microperthite, and 

 nephelite. These minerals crystallized approximately in the 

 order named. They are present in the following proportions 

 by weight : 



Albite 79-34 per cent 



Micropertbite 3-03 



Nephelite 3-27 



Biotite 11-94 



Calcite 2-42 



100-00 



*F. D. Adams and A. E. Barlow, Memoir No. 6, Canada Geol. Surv., 

 1910, p. 321. 

 fP. D. Qnensel, Bull. Geol. Inst, of Upsala, vol. xii, p. 135, 1914. 



