154 The ^l HI erica II Geoloyist. September, i«9r> 
masses arc Ix'licvcd to l)c wholly of tliis a,a,'('. Tlic writer has 
discussed the ])re-Keweenawan aj^e of tliis ^ahhro ()uite fully, 
based on Lawson's report and vivid illustraticuis from photo- 
j;rai)]is, in Bulletin K. of the Minnesota survey, and the results 
of later field work in northeastern Minnesota have only served 
to supply details entirely consistent Avith this j^-eneral distinc- 
tion. The basal conj^lomerate at Grainl Portage island con- 
tains pebbles from these eruptive rocks as well as from the 
hardened elastics of the Animikie adjacent. The great gab- 
})ro dikes which cut the Animikie about Grand Portage bay, 
rising abruptly, as in Mt. Josephine and Hat point, from three 
hundred to a thousand feet above lake Superior, extend from 
Pigeon point characteristically across the Indian reservation 
and to Brule lake. At this point the slates are hardened into a 
''black rock," or are rendered vesicular, but are distinguisha- 
ble as members of the Animikie. The details of the extension 
of these eruptives to Duluth cannot be given here. Suffice it 
to say that as a grouj) they appear on the lake shore at many 
places, and apparently Howed as lava sheets. They consti- 
tute the felsytes at Grand Marais, and at Baptism river and 
lU'ar Duluth. They easily furnish pebbles on the lake beach. 
This group seems to constitute the most of the shore on the 
north side of the lake, in Minnesota, leaving much less of the 
Keweenawan proper than has been supposed. The later Ke- 
weenawan erujjtives invaded these eruptives in the form of 
laccolites and of dikes. Thegabbro is frequently cut by them. 
The beautiful display of these later Keweneewan basic erupt- 
ives at the red rock ])oint east of the " Eastern palisades " 
nuiy be mentioned. The trap sheets that pass about and un- 
derlie the " Great palisades" are of later Keweenawan, the 
])alisades themselves being pre-Keweenawan. The red islands 
at and east of Beaver bay are pre-Keweenawan. At Beaver 
bay and eastward from there the later traps hold many pieces 
of the earlier eruptives, both basic and acid, which they have 
derived from them in Howing along. These have been noted 
by several geologists. 
The reader is referred to a fuller discussion of this question 
in the introduction to Bulletin VllI, of the Minnesota survey, 
where also is presented evidence of a similar separation in 
Wisconsin and Michigan. 
