LE BASIC MASSIVE RO CICS, 2 LC, 3 
tion another that reveals itself as a series of very fine lines parallel 
to the coarser lines of the prismatic cleavage. Its inclusions are 
little particles of magnetite, small plates of biotite, tiny masses of 
green and brown earthy matter and a few glass particles. 
The existence in these rocks of an aggregation of many small 
rounded grains of augite in the place of the large plate of this 
mineral in the true gabbro is strongly suggestive of the polyso- 
matic augites discovered by Lawson’ in the diabase of certain 
dikes in the Rainy Lake region, Canada. Inthe Minnesota rocks 
the polysomatization of the augite seems to be an intermediate 
step in the granulitization of the gabbro, not, however, in the sense 
that all the granulitic rocks have passed through this stage at 
some time in their history, but in the sense that the polysomatiza- 
tion of the augite is the result of a force similar in character to 
that which produced granulitization in the granulitic rocks but 
less efficient in its action. 
The plagioclase of these rocks is in allotriomorphic grains of 
varied sizes and of very irregular shapes in those portions of 
sections that are poor in augite, and in small and more or less 
rounded grains where rounded augites and olivines are found. 
For the most part the feldspar is quite fresh, but here and there 
little accumulations of kaolin occur in it, and small bunches of 
green chloritic substance fill the interstices between the neighbor- 
ing grains. Under low powers all the plagioclase appears to be 
filled with dust, but this dust under high power is resolved into 
long needles and small plates of opaque or dark brown sub- 
stances, and tiny irregular glass inclusions. A few long, narrow, 
quadrangular cavities and some elliptical ones seem to be filled 
with liquid, but they are in all cases so minute that it cannot be 
certain that this is the case. AMll the inclusions of this character 
are usually heaped toward the centers of the feldspar grains, with 
a zone of clear plagioclase around them. In addition to these 
inclusions there are also imbedded in the feldspar a few rounded 
grains of augite, and of magnetite, and along the edges of the 
last named mineral flakes of reddish brown biotite. 
tProc. Can. Inst. 1887, Toronto, 1888. 
