4 MET KOWIIMAIL, QU CLE OIIOG 4, 
As to the nature of the plagioclase it is difficult to draw 
accurate conclusions. Measurements of the extinction angles of 
contiguous twinned lamelle indicate a labradorite. The most 
noticeable difference between the plagioclase of these rocks and 
that of the true gabbro is with respect to their twinning bars. In 
the latter rock the lamelle are broad and but few in number, and 
but one set occurs. In the granulitic rocks the striations are 
narrow and very numerous. Moreover there are two sets of them 
inclined to each other at angles of about go”, and the lamelle in 
each set frequently wedge out toward the interiors of the grains 
in which they occur. Again, small areas near the centers of 
grains will often have two sets of lamelle crossing each other, 
while in other portions of the same grains but a single parallel 
series is found. Such phenomena as these are usually interpreted 
as pointing to a secondary origin for much of the twinning in plagi- 
oclase. In the present instance a secondary twinning accom- 
panying the granulitization of the rock would indicate that both 
phenomena owe their existence to common causes. Since the 
rocks are not sheared, the only causes that can be assigned for 
them are motion within the rock mass and strains produced by 
rapid and irregular cooling. 
The magnetite, as has already been said, is to be found as 
small grains included in all the other primary components, and 
also as irregular masses between them. Whenever it comes in 
contact with plagioclase, there is formed around it a reaction rim 
of biotite. 
There seems to be no definite order of succession in the 
formation of the various components. Sometimes the order is 
magnetite, olivine, pyroxene and plagioclase; at other times 
the plagioclase is older than the pyroxene while younger than 
the olivine, and again in a few instances the feldspar appears to 
be even older than the olivine. With respect to the age of their 
feldspar the granulitic rocks occupy an intermediate position 
between the gabbros and the diabases, in the former of which 
rocks the plagioclase is younger than the pyroxene, while in the 
latter it is the older component. 
