158 E. P. CAREY AND W. 9. MILLER: 
In marked contrast to the diorites, the minerals in many of these 
gabbro-norites are clear and fresh. ‘The list of minerals in this 
series of rocks includes the following: plagioclase, hypersthene, 
diallage, enstatite, hornblende, olivine, augite, and iron-oxide. Some- 
times all of these may be seen in a single section. 
Plagioclase, chiefly labradorite, is the most.constant of the min- 
erals present. It occurs in clear glassy plates the crystals being 
usually well-defined. Twinning according to both the albite and 
carlsbad laws is common. Sometimes pericline twinning was 
observed. Olivine and hypersthene are occasional inclusions. 
Hypersthene is the second most abundant mineral in the typical 
norite. Very little, or sometimes none, is present in the gabbro. 
The hypersthene usually appears as allotriomorphic crystals. The 
pleochroism from reddish-brown to greenish-yellow to green is very 
distinct. The hypersthene seems generally rather fresh but some- 
times it is weathered to a green serpentinous mineral. 
Diallage is the next most common mineral in the typical gabbro, 
but is less abundant in the norite. It appears as large irregular 
crystals, often blurred by weathering. In ordinary light it varies 
from nearly colorless to a light green. ‘The fine striations so char- 
acteristic of diallage are well developed. The crystals exhibit a 
metallic sheen and show no pleochroism. In a few instances twinning 
was noticed. Plagioclase is often included in the diallage, and very 
often the diallage has grown partially around the plagioclase, thus 
showing it to be later in formation. 
Enstatite is abundant in some of the gabbros. It always occurs 
without regular crystal boundaries. The highly characteristic 
columnar structure and the parallel extinction are well shown. 
Hornblende is usually absent from the typical gabbro; it is pres- 
ent to only a small extent in the norite; but in sections from a few 
outcrops it is so predominant that the rocks may readily be called 
hornblende-gabbro. In the latter rocks much of the hornblende 
is badly weathered and is altered to cholorite in green patches. ‘The 
characteristic cleavage lines making angles of about 124° are very 
distinct in the primary hornblende. It exhibits a pleochroism from 
a green to a light yellow. Examples of twinning are -also quite 
common. 
