The Keweenaivan i?i Minnesota. — Elftmati. 145 
the normal phase of the rock. The next variety is generally 
closely associated with this. 
Peridotyte. This consists chiefly of olivine together with 
some pyroxene. The pyroxenyte and peridotyte are quite 
limited in extent. The rocks of this variety found along the 
northern boundary of the gabbro are not part of that rock, 
but are referred to the contact action of the gabbro upon the 
older rocks, 
Mag7ietite. Small masses of titaniferous magnetite 
are scattered throughout the gabbro. Extensive masses are 
known only along the northern border and in the eastern 
part of the gabbro. These deposits of magnetite are espe- 
cially numerous in the region between Brule lake and the 
northern limit of the gabbro. The ore bodies are found in 
three belts running east and west. The northernmost follows 
the boundary of the gabbro. The second runs through the 
southern part of township 64 north, and the southern or third 
belt runs south of Brule lake through the central or southern 
part of township 63 north. 
The magnetite deposits are usually associated with granu- 
htic noryte, which is always slightly the older of the two. 
The noryte is considerably broken and traversed by veins of 
magnetite extending from the large masses around its edge. 
From the main mass of the magnetite, stringers and apophyses 
run several hundred feet into the massive gabbro. Frequently 
the magnetite occurs in numerous parallel bands several 
inches to a foot in width, which alternate with bands of the 
associated gabbro. As many as twenty-five of these bands 
have been noticed within a belt ten feet wide. There are all 
proportions of minerals between magnetite and the normal 
phase of the gabbro. The variations of the ore as seen in a 
shaft 19 feet deep on section 2i,T. 63 N., R. 4 W., is as follows : 
At the surface the rock was composed of solid coarse magne- 
tite stained green with a coating of malachite. The pure mag- 
netite continued downward for five feet when a few grains of 
chalcopyrite, pyrite and plagioclase were found. At seven 
feet below the surface the magnetite became fine grained, and 
a small amount of plagioclase and pyrite continued. Olivine 
appears as bright, yellow grains. Continuing downward the 
plagioclase and pyrite disappeared and the lower ten feet of th^ 
