Gabbroid Rocks of Minnesota. — Wincliell. 153 
Chapter VII. Cordierite noryte. 
1. Geological occurrence. 
2. Exterior cbaracters. 
3. Texture and mineralogical composition. 
4. Detailed study of tlie minerals. 
1). Labradorite. 
2). Bronzite and enstatite. 
3). Anomite. 
4). Cordierite. 
5). Quartz. 
6). Magnetite and pyrite. 
7). Staurolite and graphite. 
8). Zircon. 
9). Apatite, epidoto, and spinel. 
10). Anthophyllite and muscovite. 
f). Chemical composition. 
6. Origin. 
Chapter VIII. Quartz gabbro. 
1. Geological occurrence. 
2. Exterior characters. 
3. Texture and mineralotrical composition.* 
4. Detailed study of minerals. 
n. Cl>emical composition. 
6. Origin. 
Chapter IX. Silicoferrolyte. 
1. Geological occurrence. 
2. Exterior characters. 
3. Texture and mineralogical composition. 
4. Detailed study of the minerals. 
5. Chemical composition. 
6. Origin. 
('hapterX. Resume and conclusions. , 
1. Comparative petrographic study. 
1). Normal type. 
2). Modifications due to: — 
a). Conditions of solidification. 
b). Original heterogeneity or differentiation of magma. 
c). Contacts (eudomorphism and exomorphism). 
3). Classification. 
2. Comparative mineralogical study. 
3. Comparative chemical study. 
1). Methods of analyses. 
2). Results of analyses. 
3). Graphic representation of analyses. 
a). Method of Micliel L6vy. 
b). Method of Hriigger. 
c). Method of Recite. 
d). Method of Iddings. 
Introduction. 
The great continental nucleus, which Dana has called the 
"North American protaxis," extends, as is well known, from 
the eastern limits of Labrador to the head waters of the Mis- 
sissippi river and from New York state to the Arctic islands of 
