TJie Keivecnazvan in Minnesota. — Elftrnan. i8i 
Lawson/" in 1893, shows that the trap sheets associated 
with the Animikie slates are intrusive siUs whose age is con- 
sidered to be post-Keweenawan (Keweenian). On the Cana- 
dian side of lake Superior these sills were found in the Ke- 
weenawan, and the author states his opinion, "that many of 
the heavy sheets of dark diabase or gabbro which prevail on 
the Minnesota coast, particularly in its eastern portion, and 
which have been described and referred to by former ob- 
servers as volcanic flows of Keweenian age, are laccolitic 
sills." 
Bay ley,'" in 1893, gives in detail the petrography, rela- 
tions and field occurrences of the eruptive and sedimentary 
rocks of Pigeon point. Bayley," reviews the basic, massive 
rocks of the lake Superior region. The great gabbro of 
northeastern Minnesota, whose petrographical characters arc 
described with considerable detail, has a typical granitic struc- 
ture and shows the characters of an intrusive rock. It differs 
essentially from all of the basic intrusive rocks of the Anim- 
ikie and from all other Keweenawan basic rocks, none of 
which have a typical granitic structure. Along the northern 
border of the gabbro are peculiar basic and quartzose rocks 
which are regarded as peripheral phases of the gabbro. The 
author concludes that further field work will probably show- 
that the gabbro is either a batholite, well toward the base of 
the Keweenawan series, or that it is an eroded mass upon top 
of which the later Keweenawan beds have been' deposited. 
Grant,^ in 1894, states that the gabbro varies in miner- 
alogical composition, at times being entirely composed of 
feldspar and again exceedingly rich in olivine. The gabbro 
contains fragments of the Animikie slates. The fine grained 
gabbros are older than the main mass of the gabbro. The 
acid eruptives in the vicinity of Brule lake are later than the 
gabbro and probably represent the deep seated magmas that 
produced the extensive acid surface flows seen along the Min- 
nesota coast. 
Elftman," in 1894, divides the Keweenawan into the 
gabbro, diabase, red rock and later dike groups. The anor- 
thosytes of the Minnesota shore of lake Superior are shown 
to be detached blocks inclosed in later trap rocks, and they 
do not represent the eroded surface of an older formation. 
