TJie Kcweenawan in Minnesota. -Elftinan. 179 
Wadsworth/" in 1887, gives petrographical descriptions 
of many of the Keweenawan rocks. 
Irving,™ in 1887, emphasizes the structural break be- 
tween the Huronian and the Keweenawan formations. ,The 
Potsdam sandstone rests upon the eroded surface of the Ke- 
weenawan. The same author,"' in 1888, pubHshed a geo- 
logical map of northeastern Minnesota. The Keweenawan 
is divided into two large divisions, the basal gabbro and the 
remainder consisting of the upper five groups described in 
1883. 
Winchell (Alex.)," in 1888, gives further details of the 
gabbro area along its northern limit. 
Winchell (N. H.),'^ in 1888, describes the rocks along 
the northern boundary of the gabbro from Gunflint lake west- 
ward. The trap (gabbro?) lies upon the Animikie in many 
places. The gabbro lies upon the Pewabic quartzyte and the 
Keewatin formations. The Pewabic quartzyte is placed above 
the Animikie. The same author,'' in 1889, gives a summary 
of the results of work on the crystalline rocks in northeastern 
Minnesota. The gabbro, red rocks and Keweenawan rocks 
are referred to the Paradoxides horizon of the Potsdam age. 
In general the conclusions and facts presented agree with 
those expressed in earlier reports. 
Winchell (H. V.),"" in 1889, gives many details regard- 
ing the geographical distribution of the Keweenawan. The 
gabbro embraces large fragments of Animikie quartzyte and 
slate, thus showing its later origin. The gabbro is intersected 
by greenstone dikes, and in places gave the impression that 
it is on top of the Cupriferous, and hence more recent. 
Grant,'" in 1889, gives numerous details regarding the 
geographical extent of the Keweenawan. The gaburo is cut 
by veins or dikes of syenite, and the contact between these 
rocks is always distinct. Portions of the Animikie beds are 
included in the gabbro. 
Winchell (N. H.),"' in 1889, considers the basic eruptives 
consisting largely of gabbro and following the Animikie, and 
those of the Cupriferous formation as representing separate 
epochs of eruptive activity. 
Winchell (N. H. and H. \'.)," in 1890. describe tlie 
gabbro titaniferous magnetites of the Mesabi range. 
