422 PECK 



and shows about equal amounts of feldspar and augite with a 

 sprinkling of biotite scales. 



In microscopic thin section the rock is seen to have as its 

 most prominent constituent hypidiomorphic augite, having the 

 peculiar green tinge of the soda bearing variety. On separa- 

 tion with Toulet's solution it gave the following analysis : 



SiO^ 



= 



50-55 



FeO^ 









7.27 



Fe,03 





AlA 



= 



S.66 



MgO 



= 



11.00 



CaO 



= 



19.70 



Na^O 



= 



1.70 



K,0 



= 



.48 



99-36 



which shows an approach to an a^girine augite.^ 



The allotrimorphic feldspars, as a rule about equal in quantity 

 to the augite, consist usually of microperthitic intergrowths of 

 albite or oligoclase and orthoclase. The feldspars generally 

 show a wavy extinction due to pressure and frequently the con- 

 fused, patchy intercrystallization seen in many syenites contain- 

 ing nearly equal amounts of both soda and potash. On isolation 

 the feldspars were shown by an alkali determination to contain 

 8.04^ of potash and 4.55^^ of soda.^ The last constituent of 

 importance is biotite which in one locality quite replaces the 

 augite and the rock thus becomes essentially a mica syenite. 

 Magnetite occurs in but limited quantities. Long prisms of 

 apatite are quite abundant in places and were as usual among 

 the first crystals to form, being included in both the biotite and 

 augite. 



1 This separation and analysis was made by Mr. Fred H. Moffit, post-graduate 

 student in geology and assistant in chemistry in Lafayette College, Easton, Pa. 



2 This determination was also made by Mr. Fred H. Moffit. 



