382 The American Geologist. December, 1904. 
The Cincinnati island afforded a partial barrier to the drifting 
of the sediment into the clearer Osage waters beyond. 
At the close of the calm Osage age came a series of uplifts 
and depressions, whose effects are seen in the Mis^ssippi valley 
and at the east. The St. Louis limestone was formed in waters 
extending 200 miles further north than those of the Osage, 
and this northward extension was followed by a retreat of 400 
miles to the south. 
In the eastern part of the Waverly gulf, the changes began 
earlier than in the Osage gulf, and the coast line, according to 
Lane,* receded westward from western New York and central 
Pennsylvania, until a large part of Ohio and Indiana were out 
of water by the end of the Marshall or Waverly age. This left 
the Michigan basin enclosed between the mass, of land at the 
northeast, and probably also at the northwest, and the low land 
over northern Ohio and southern Michigan.! 
On the south side of this low land were deposited the sedi- 
ments forming the coarse sandstones and conglomerates of the 
Logan group laid down irregularly in Ohio with an average 
thickness of 200 feet. To the north side wete deposited the 
sediments forming the rocks of the Michigan group, shales, 
limestones, and beds of gypsum. 
The Mississippi extension of the St. Louis is represented in 
Michigan by the Bayport limestone, in Ohio by tne Maxville^ 
which come above the Michigan group. TbiS group would 
correspond in time with the Burlington and Keokuk, or the 
Osage (Augusta) of the Mississippi valley. The thickness of 
the group in Michigan is 232 feet (Lane, Vol. VII, Part II, p. 
16), the Augusta in Iowa is 230 feet, the Logan in Ohio is 200 
feet. 
MICHIGAN GROUP. 
The Carboniferous, Bayport, or St. Louis, Innestone in 
Michigan is also called by Lane the Upper Grand Rapids ser- 
ies, and the Michigan group is known as the Lower Grand 
Rapids. 
At Grand Rapids, the typical locality for the section, the 
lower series outcrops to the south of the city as a group of 
shales, thin bedded limestones, and gypsum layers, while the 
• Michigan Geological Survey, vol. vii, part II, p. 15. 
t The extension of the Cincinnati island above mentioned. 
