CHEMICAL COMPOSITION. 249 
I, I, and III. Dikes 27, 29, and 9 respectively, selected to represent the mean 
and the extremes of composition. Analyses by E. W. Morley.* 
IV. Dike described by Eakle from Upper Chateaugay lake. American Geologist, 
July, 1893, page 31. Analysis by A. S. HBakle. 
_V. Keratophyr from Marblehead Neck, Massachusetts, described by J. H. Sears. 
Bulletin Museum Comparative Zoology, vol. xvi, no. 9, page 170. Analysis by T. M. 
Chatard. 
VI. Bostonite from lake Champlain by Kemp and Marsters.  Bullettn United 
States Geological Survey, no. 107, page 20. Analysis by J. F. Kemp. 
VII. Nordmarkite (quartz-bearing syenite with low iron per cent) described by 
Brogger from north of Christiana at Touseniis. Analysis by Forsberg. 
Discussion.—Dike 29, column II, was selected as probably representing 
the most acidic of the dikes. The thin-section shows an unaltered rock 
composed of microperthite, quartz, and specular hematite, with such 
slight amounts of apatite and chlorite that they may safely be neglected. 
For purposes of calculation the slight amounts of manganese and mag- 
nesia are neglected. 
Calculation of Analysis IT 
Molcculey Orthoclase. | Albite. | Anorthite. | Quartz. | Hematite. 
GO ine eee 1149 318 528 18 OAS hah (Mele hase 
INWOn cohen pee 150 53 88 Oye alls ante anes: Selly yae Rape 
Owes... SHEN Cn ate age PRAT UY ome CO ew 20 
CAO seeks. Te alles ers eye eee pe | Meera eee Qa rolliee e Ree bn ssee ised 
IK (O}ohero cee 53 Cee RRS ol) eae mma all eee ym aliens Maka ey 8 
INEVAO) con aioe caer hs} ahi eieco ie Rrosnorcaeen SOR P omiae he, ca esnile) ascent sroealla weber yates 
1474 424 704 36 285 20 
29.49 % | 46.09 %| 2.48% | 17.11%] 3.98% 
Both apatite and calcite are present in slight amount—probably in 
sufficient quantity to account for the excess of lime, which amounts to 
only 0.27 per cent of the rock. The feldspar is seen to have the approx- 
imate composition, Or,Ab,, the plagioclase being albite, Ab,,An,. The 
composition of the feldspar, recalculated to 100 per cent, will be as 
follows: 
SiO MRE at Gp reg 55 8 aN a a 65.93 
PAIR OMe eer tte incre SNe NE ee 20.15 
(GENO)! 5 Gosia Se ran rene Hin eee eRe ce IG eh, 0.62 
GO) c.d3 SSG rer de nercae aetna ce a cat 6.37 
ING O)ssbi dato Oem eS RE rake RRS EC cr 6.93 
which agrees well with the published analyses of microperthite and an- 
orthoclase, except that in the latter the soda is often more in excess of 
*The chemical analyses were made by Professor E. W. Morley, of Western Reserve University, 
whose hearty cooperation I gratefully acknowledge. 
