408 Pirsson — Petrography of Tripyramid Mountain. 



Apatite 0*5 Texture. The rock has a thor- 



Iron ore .. — 4*0 owghly normal granitoid texture, 



Biotite 1*0 and shows no tendency to the 



Angite .- 1*0 trachytoid one so often exhib- 



Hornblende G'O ited by alkali C syenites. The fab- 



Labradorite 6*5 ric is inequigrannlar-seriate, and 



Microperthite 80*0 consertal, composed of irregular 



Quartz TO nearly equant grains. 



Total 100-0 



Chemical Composition. — For the chemical analysis of this 

 rock, and also of others given later, I am indebted to the late 

 Mr. C. J. Monahan, a promising young chemist, who at one 

 time was assistant in the Sheffield Chemical Laboratory. It is 

 given in the adjoining table, and the analyses of some other 

 closely related syenites are quoted for comparison. 



Analyses of Syenites. 



I II III IV V VI VII 



SiO, 62-12 63-71 62-99 59'01 63-20 60"60 1-035 



Al„0,.-_ 17-57 16-59 14-25 18-18 17*45 16-79 -173 



Fe",O s .. 2-16 2-92 2"78 1-63 ) 2"77 -014 



FeO ... 2-59 0-66 5'15 3-65) 2'17 '036 



MgO... 0-86 0-90 1-30 1-05 0'75 2-14 -021 



CaO 2-37 3-11 2-72 2-40 1-40 4-47 -043 



Na,0... 6-78 826 4-86 7*03 6"90 4-40 '110 



K 2 4-79 2-79 6-35 5-34 5-88 4'57 -051 



H 2 0+.- 0-48 0-19 0-18 0-50 -50 0*61 



H„0— .. 0*09 .- 0-15 0-25 



Ti"0 2 ... 0-84 0-86 0-16 0-81 0-46 0'90 '010 



P 2 6 0-23 tr 0-28 '001 



MnO... tr. 0-20 0'18 0'03 0-15* 



Total... 100-88 100-19 100-92 99-95 100-14 100-10 



*BaO. 



I. Syenite, var. Umptekite, Tripyramid Mt. C. J. Mona- 

 han, analyst. 

 II. Syenite, var. Umptekite. Shore of the Umpjavr, Kola 

 Peninsula, Lapland. W. Ramsay, Fennia 11, No 2, 

 p. 205, J 894. W. Petersson, anal. 



III. Syenite, var. Umptekite, Beverly, Mass. F. E. "Wright, 



Tscher. Mitt, xix, p. 318. F. E. Wright, anal. 



IV. Syenite, var. Umptekite, Red Hill, New Hampshire. 



"W. S. Bayley, Bull. Geol. Soc. Amer., iii, p. 243, 



1892. W. F. Hillebrand, anal. Total includes BaO 



0-08, CI 0-12. 



V. Syenite, var. Nordmarkite, Tonsenaas, Norway. Brog- 



ger, Zeit. f. Kryst, xvi, p. 54, 1890. G. Norsberg, anal. 



VI. Syenite, var. Plauenite, Plauen near Dresden, Saxony. 



Anal., H. S. Washington. This Journ., xxii, p. 129, 1906. 



VII. Molecular proportions of No. 1. 



