The Keiveenawan i?i Minnesota. — Elftman. 133 
follows a southwesterly course, through section 6, T. 62 N. 
R. 2 W., and through section 15, T. 62 N. R. 4 W. on the 
east branch of the Temperance river; continuing westward it 
passes through the central part of T. 60 N. R. 6 W. between 
lakes Harriet and Bellissima; thence through the southeastern 
part of T. 60 N. R. 7 W. and between West Greenwood lake 
and Greenwood Mt., in T. 58 N. R. 10 W. At the last lo- 
cality it turns sharply toward the south, passes near the north- 
west corner of section 19, T. 55 N. R. 11 W. and from there 
continues in a southwesterly direction to Duluth. Theses 
boundaries give the widest areal distribution of the gabbro. 
Within this area are other rocks, some of which are quite ex- 
tensive and nearly all of a later geologic age. The chief area 
of this kind is the region west and southwest of Brule lake. 
Age of the gabbro. The gabbro has been assigned 
geological positions from the base of Aniniikie to the middle 
of the Keweenawan. Dr. W. S. Bayley (41, vol. T, p. 695) 
summarizes the various views and concludes that, "so far as 
the little evidence at hand enables us to judge, the gal^bro 
* * * forms a great mass of enormous extent above the 
Animikie, but below the interbedded flows and fragmentals 
of the Keweenawan series in Minnesota." After a discus- 
sion of the petrographical characters of the gabbo in which 
the intrusive character of the rock is emphasized. Dr. Bay- 
ley concludes that, "further field work on the geological rela- 
tionship of the mass will probably show either that it is a 
batholite within the Keweenawan series, well toward its base, 
or that like the anorthosites of Lawson it is an eroded 'mass- 
ive' upon the top of which the later Keweenawan beds have 
been deposited." 
All the writers upon this area, now agree that the gabbro 
is younger than all of the formations with which it comes into 
contact on its northern edge. The gabbro cuts across the 
strike of the several formations, penetrates and incloses frag- 
ments of them. In places the older rocks were completely 
changed at the time of the intrusion of the gabbro mass. On 
its southern edge the gabl)ro member is in contact with the 
later members of the series. The red rock member is the most 
common of the series. Large bosses and dikes of augite 
syenite and granite cut the gabbro near the contact of the main 
