36 WILLIAM J. MILLER 
A brief statement of the writer’s explanation of the origin 
of the variations in composition, structure, and texture of the 
anorthosite-gabbro body will now be given. 
t. It is believed that the intrusion of the anorthosite-gabbro 
magma was a complicated process of considerable duration. Much 
of the magma slowly solidified as a normal, moderately coarse- 
grained to medium-grained gabbro with an ophitic texture. Mag- 
matic currents were practically absent from those portions. 
2. In portions of the magma there were currents or movements 
sufficiently strong to cause the minerals, especially the earlier 
crystallized ones, to be drawn out into more or less perfect paral- 
lelism. ‘This accounts for the gneissoid structure or foliation 
of considerable portions of the gabbro and anorthosite-gabbro, 
especially the medium-grained and fine-grained portions. 
3. The more or less highly foliated structures of the many 
localized zones or belts of medium-grained to fine-grained rocks 
resulted from particularly active currents in those zones. 
4. The more or less sharp alternations or variations in degree 
of foliation, and the notably varying strikes of the foliation through- 
out the area, are best explained as a result of locally developed 
differential magmatic movements or currents under conditions 
of not more than very moderate pressure. It seems impossible 
to account for such structures on the basis of pressure applied upon 
the body of anorthosite-gabbro after its final consolidation, first, 
because such pressure could not have caused notable foliation of 
certain narrow belts while adjacent masses were unaffected, 
especially in view of the fact that the highly foliated zones are not 
characterized by shearing or crushing (granulation), and, second, 
because any such pressure sufficiently strong to produce foliation 
must have been exerted in a single general direction with about 
equal force, and hence the sharp variations in strike of the foliation 
are left unaccounted for. 
5. The variations in composition are the result of differentiation 
of the anorthosite-gabbro magma before or during its consolidation. 
6. Those foliated zones or belts which show sharp variations 
in composition in layers ranging from nearly pure plagioclase to 
gabbro rich in ferro-magnesian minerals are the result either of 
