INTERNAL STRUCTURES OF IGNEOUS ROCKS 441 
any one mineral may be quite completely segregated in certain 
bands. Where the minerals of any band weather more rapidly 
Fic. 3.—Faint banding in the Duluth gabbro. These bands curve slightly, and 
a white band near the hammer divides to the left. 
Fic. 4.—Conspicuous bands of peridotite and gabbro near the base of the Duluth 
gabbro. 
than those of adjacent bands, such bands appear as grooves in the 
surface. The composition of the bands is independent of the com- 
position of the wall rocks. There are no transverse dikes or con- 
nections between bands. 
