1/8 The A/nerican Geologist. March, is^cs 
It consists of distinct beds of diabase porphyryte, diabase, 
amygdaloid, coarse grained gabbro and granite porphyry. 
4. The Agate Bay group. This group forms the coast 
line for 35 miles below the mouth of Lester river, and has a 
thickness of 1,500 feet. It consists of relatively thin beds of 
diabase, olivine diabase, diabase porphyryte, amygdaloids. 
sandstones and conglomerates. 
5. The Beaver Bay group. This group is found at both 
ends of the coast, and has a maximum thickness of 6,000 feet. 
It consists of beds of black, coarse grained, olivine gabbro. 
ashbed diabases, diabase porphyrytes, amygdaloids, red felsitic 
porphyries and granite-like rocks. 
6. The Temperance River group. This group forms the 
middle of the Minnesota coast, and has a thickness of 2,500 to 
3,000 feet. In its composition and structure it is analogous 
to the Agate Bay group. 
The igneous origin of all the rocks, excepting a few thin 
beds of sandstone and conglomerate, is emphasized. Num- 
erous faults are mentioned, but none with a displacement of 
over 100 feet were recognized. The absence of volcanic ash 
was noticed. The eruptive rocks include basic, intermediate 
and acid kinds, but there is no such chronological relation be- 
tween these as is often found in more recent eruptives. The 
series rests unconformably upon the Animikie or Upper Hu- 
ronian slates in the Saint Louis river valley and in the vicinity 
of Grand Portage bay. 
Winchell (N. H.),'" in 1884, refers the igneous gabbros 
and dolerytes, together with their metamorphic products, to 
the Potsdam formation. The same author," in 1885, finds 
the Animikie slates and quartzytes overlain by the gabbro 
and red granite of the Mesabi range, which is in turn over- 
Iain by the trap rocks of the Cupriferous. 
Winchell (Alex.)," in 1887, gives detailed observations 
made on an extensive trip in northeastern Minnesota. The 
northern limit of the gabbro was determined in a number of 
localities, and some peculiar contact rocks were noted. 
Winchell (N. H.)," in 1887, gives many details and pub- 
lishes a preliminary geological map of a part of northeastern 
Minnesota embodying the results of the field investigation up 
to that time. The gabbro lies unconformably upon the Anim- 
ikie, Keewatin and granitic rocks associated with these. 
