206 The American (ieoloyist. October, 1895 
classification embodied in the Bulletins of the United States 
Geological Surve}^ which are here examined (Nos. 81 and 86). 
They are given in descending order. 
Succession of (geological Events. 
(I.) A great sandstone, non-conformable over (a) the Archeau; (6) the 
lower iron-bearing series (Keewatin); (c) the upper iron-bearing series 
(Animikie) and its ervxptives; {d) parts of the Keweenawan. It is con- 
formably under sandstones carrying an Upper Cambrian faiina. The 
Dieellocephalus horizon. 
(II.) Disruption, folding and metamorjihosing of the rocks of No. Ill, 
accompanied by the issuing of basic molten rock, and perhaps by the 
fusion of some of the elastics. Eruptives cotemporary with and fol- 
lowed by clastic sediments of great thickness. Keweenawan eruptive 
age. 
(III.) Great qviartzyte and conglomerate, underlying the last, non- 
conformable over all the older formations, after a great erosion interval. 
The Keweenaivan basal beds, Parado.rides horizon. 
(IV.) Great vipheaval and metamorphosing of the rocks of No. V, ac- 
companied by the formation of enormous dikes and masses of gabbro 
with titanic iron ore, and of anorthosyte rock, the fusing of the elastics 
of No. V and the production of quartz-porphyries and felsytes on a large 
scale. The Animikie revolution . 
(V.) Black slates and reddish to grayish quartzytes (Wauswaugo- 
ning), iron ore (Mesabi), quartzyte. Slates sometimes converted to fine- 
grained crystalline schists and magnetited, and to gneisses. Quartzytes 
and slates changed sometimes to quartz-porphyry and keratophyre. A 
limestone, often marmorized, of greater or less thickness belongs near 
the bottom. The Animikie. Supposed OleneUus horizon. Non-con- 
formable on the different parts of the Archean. 
(VI.) An unconformable underlying complex of crystalline rocks. 
It is scarcely necessary to dwell on this statement of the se- 
quence of geological events in the Lake Superior region. This 
history has been established by the combined observations of 
numerous geologists during the last thirty years. Probably 
no geologist who is acqviainted with the region would call in 
question any of the events above expressed, or the relations in- 
dicated. There are of course many minor matters, more in 
the detail of subdivision and derivation for the different parts, 
on which geologists would not be found in accord, but the 
grand steps of the history as tabulated, whatever the age at 
which they occurred, are accepted \)j nearly all. 
Attention may now be called to the parallelism of this struc- 
tural series with that already expressed for the Adirondack 
and the Taconic areas. 
