Gabbroid Rocks of Mimiesota. — Winchell. 185 
Explanation of Plates. 
Plate VIII. 
Figure i. Olivine gabbro (1136) from Birch lake. Coarse 
granular texture. A cavity in the labradorite (3) filled with antig- 
orite (13), derived from the olivine of the rock. Crossed nicols x 100. 
Figure 2. Olivine gabbro (1136) from Birch lake. Pegmatitic 
intergrowth between labradorite (3) and augite (6), and also be- 
tween magnetite (10) and augite (6). A large mass of olivine (9) is 
occasionally xenomorphic toward the feldspar. Biotite (5) has been 
formed by mesogenesis. Crossed nicols. x 100. 
Plate IX. 
Figure i. Normal diabase (954) from Birch lake. A single 
anhedron (3') of labradorite twinned according to the four laws: 
Baveno, Carlsbad, albite, and pericline, but the last type is not visi- 
ble in the position photographed. The large labradorite crystals are 
separated by stringers of twinned pyroxene (6). Crossed nicols. x 100. 
Figure 2. Olivine diabase (1843) from Pigeon point. Ophitic 
texture very distinct. Labradorite (3), pyroxene (9), olivine (6), and 
bowlingite (14). Crossed nicols. x 75. 
Plate X. 
Figure i. Plagioclasyte (336E) from Carlton peak. Augite (16) 
surrounded by magnetite (10), and by satellites of augite, oriented 
on the principal pyroxene mass. A large automorphic crystal of 
magnetite (lo), decaying labradorite (3), and fibers of zeolites (19) 
colored by hematite also occur. Natural light, x 100. 
Figure 2. Plagioclasyte (336E) from Carlton peak. Rectangu- 
lar alteration of labradorite. This alteration is endogenetic, and 
results in the formation of zeolites, and, later, calcite, zoisite, hema- 
tite, etc. Natural light, x 100. 
Plate XI. 
Figure I. Silicoferrolyte (960) from Birch lake. Magnetite (10) en- 
closes, in poikilitic texture, fayalite (9), augite (6), and quartz (i). 
Crossed nicols. x 100. 
Figure 2. Orthoclase gabbro (1797) from Duluth. Orthoclase 
(2) surrounds and traverses the labradorite (3), which encloses crys- 
tals of augite (6) and apatite (11). Crossed nicols. x 100. 
Plate XII. 
Figure i. Cordierite noryte (983) from Sec. 15, T. 63-9. Poiki- 
litic texture. Quartz (i), labradorite (3), cordierite (4), anomite (5), 
bronzite and enstatite (8), and anthophyllite (15). Crossed nicols. x 
100. 
