1 86 The Americafi Geologist. September, ]90(» 
Figure 2. Quartz gabbro (8S4G) from near Little Saganaga 
lake. Very small rutiJe crystals in groups, in penninite (12). Sec- 
ondary calcite (16). Secondary quartz in the edge of the chlorite 
oriented on the magmatic quartz (i), forming an "enlargement." 
Crossed nicols. x 100. 
Plate XIII. 
Graphic representation of the chemical composition of the rocks 
studied by the method of Michel Levy. SiO;!^ expressed in figures; 
AI2O3 not directly expressed, unless in excess which=a; FeiOa^f: 
FeO^f; CaO, feldspathisable,=c; CaO in excess=c'; NajO=n; 
K.O=k. 
Figure i. Silicoferrolyte (960) from Birch lake. 
Figure 2. Troctolyte (514) from near Duluth. 
Figure 3. Olivine gabbro (1136) from Birch lake. 
Figure 4. Normal diabase (954) from Birch lake. 
Figure 5. Orthoclase gabbro (1797) from Duluth. 
Figure 6. Olivine diabase (1843) from Pigeon point. 
Figure 7. Plagioclasyte (336E) from Carlton peak. 
Figure 8. Cordierite noryte (983) from Sec. 15, T. 63-9. 
Figure 9. Quartz gabbro (854G) from near Little Saganaga 
lake. 
Figure 10. Pyroxene from olivine diabase (1843) from Pigeon 
point. 
Figure 11. Labradorite from plagioclasyte (336E) from Carl- 
ton peak. 
Figure 12. Pseudomesolite (with HuO omitted) from plagio- 
clasyte (336E) from Carlton peak. 
Plate XIV. 
Graphic representation of the chemical composition of the rocks 
by the method of Brogger. 
Figure i. Average of olivine gabbro (1136), diabase (954) and 
olivine diabase (1843). 
Figure 2. Plagioclasyte (336E). 
Figure 3. Quartz gabbro (854G) 
Figure 4. Silicoferrolyte (960). 
Figure 5. Cordierite noryte (983). 
Figure 6. Troctolyte (514). 
Figure 7. Orthoclase gabbro (1797). 
Plate XV. 
Graphic representation of the chemical composition of the rocks 
by the method of Bec.ke. Si is located by the sign a ; Al, by the sign 
X; Fe, by the sign ■; and Mg, by the sign +; Ca, Na, and K de- 
termine the position of the basal point in the "horizontal field" (low- 
er figure). I. Silicoferrolyte (960); 2. Troctolyte (514): 3. Olivine 
