CHEMICAL COMPOSITION IN SEDIMENTS 469 
no representatives of this order among the igneous rocks of Washing- 
ton’s tables. Others among these schists show quartz in excess of the 
proportions given above as characteristic of igneous rocks. 
EXAMPLES OF THE APPLICATION OF CHEMICAL CRITERIA 
In conclusion, the application of the criteria which have been con- 
sidered to certain type examples may aid in a fuller understanding 
of the principles involved. 
The two gneisses described by Adams’ from St. Jean de Matha 
and from Trembling Lake in Quebec show both a dominance of 
MgO over CaO and of K,O over Na,O. Both show more than 
ro per cent. of corundum in the norm and thus fall in sub-class IT of 
class II, characterized by only 4 doubtful analyses in Washington’s 
tables. Adams’ conclusion that they are of sedimentary origin would 
appear therefore to be well grounded. 
I 2 3 4 
SiO fara. o 60.33% 64.89% 78.90% 78.28% 
INAO a5 oa 6 Ob 20.85 13.10 I2.20 9.96 
Fe,03. 3.59 4.99 ane THOS 
He @ are 4.47 0.99 3 1.78 
INERO)oomono bon 2.07 B78 0.75 0.95 
CAO ais che 1.82 1.95 0.25 1.68 
INGOs a ame ae L138 2.68 2.30 278 
KE Ole ae so aces 2.84 5-46 0.24 1.35 
BAO) Cpe oma eer 1.60 0.83 
He Or ee ik Bue) One Seo 0.12 
BaO ice ccsnes te cae ives ace eis 
ARKO bs raeealeaae I.4I 0.98 0.50 0.70 
otal em IOr.82%* 100.49% 99.40% 100.44%fF 
* Includes P,0;—o. 28 per cent. 
+ Includes P,0,—o.11 per cent., MnO—o.08 per cent., and BaO—o.02 per cent. 
No. 1. Gneiss from near Jenkintown Junction, Penn. Described as containing 
garnet, mica, feldspar, and magnetite. F. A. Genth, Jr., analyst, Penn. Geol. Survey 
Report, C®, p. 122. 
No. 2. Muscovite-biotite gneiss from Pfelderstal, Tirol. Paul Seidel, Beztrage 
sur Kenntnis der gesteinsbildenden Biotite, Borna-Leipzig, p. 47, 1906. 
No. 3. Muscovite gneiss from near Zell in the Fichtelgebirge, Bavaria. Rosen- 
busch, Elemente der Gesteinslehre, 2d ed., p. 488 (1901). For calculation of the norm the 
iron is apportioned as Fe,O,;—1.32 per cent.—and FeO—o.98 per cent.—which is 
about the ratio of the two oxides in the average of the pelite schist analyses. 
No. 4. Gneiss, Great Falls, near Washington, D.C., Fifteenth Ann. Rept., U.S. 
Geol. Survey, p. 670 (1895). 
t American Journal of Science, 3d series, Vol. L, p. 67 (1895). 
