MeethKj of the American Asso<-l((fiou. — UpJiam. 235 
river in southwestern Ohio, we have a perfect and unbroken series mark- 
ing stages in the retreat of the last ice-sheet from near Cincinnati to 
the strait of Mackinac. 
Beginning at Leverett's most southerly moraine, near Cincinnati, and 
numbering the series northward, along the central axis of the Great 
Miami valley, down that of the Maumee, up that of the Detroit and St. 
Clair rivers, and thence northward along the east shore of Michigan, 
we find that the fifteenth or Hagenville moraine lies just south of the 
strait of Mackinac, and that the thirteenth or Huron-Saginaw moraine 
lies a little back from the shore of Saginaw bay and the south arm of 
lake Huron. That the first moraine back of the shore in each of these 
latter valleys is in reality one continuous moraine, bending northward 
around the " thumb " and marking strictly contemporaneous positions 
of the ice front, was a subject for proof by observation. This fact was 
established 1)y a detailed study f)f the moraines near Ubly. The tirst 
moraines of the two valleys join in a right angle near this place, the Sag- 
inaw moraine running to the northeast to join the Port Huron moraine 
which comes up from the southeast. The angle is sharp and the forms 
of the moraines are quite simple, leaving no doubt as to contempora- 
neity. 
In making the count of moraines, the central axis or line of least 
resistance in the valleys was followed in order to avoid the confvision of 
moraine knots. The oscillations of the ice front were there freest, and 
in the present case the line indicated from Cincinnati to Mackinac has 
no moraine complex. The series appears to lie complete and without 
omission. 
If we turn northeast at Toledo and pass down the axi.s ui lake Erie 
and over into the lake Ontario basin, nuraljering Leverett's moraines 
as we go from the Toledo moraine as the eleventh, we shall find that 
the Albion moraine in western New York is the fifteenth. The interval 
remaining V)etween the Cleveland and Hamburg moraines is so great as 
to suggest a possible omission of one memljer. But this is hardly 
likely. The Lockport moraine as the fourteenth corresponds to the 
Alcona moraine of Michigan, the fourteenth on the northward line. 
The fourteenth and fifteenth moraines undoufjtedly pass along the 
south side of Georgian bay between lakes Huron and Ontario : and one 
or the other of these two proVjably records the ice harrier of lake Warren 
in its last stage. 
The more imjjortant conclusions suggested by this pajxT were noted 
only very brietly. The irregularities in the moraine series are so simple 
that they are nearly all readily accounted for by the topographic fea- 
tures in the jjath of the moving ice-sheet. Such being the case, it 
becomes plain that if the irregular features of the land had been absent 
the moraine series would have been nearly if not perfectly regular. 
These characters point to the following conclusions: first, that the os- 
cillations of the glacial recession were regular, periodic variations, su- 
perimposed upon the main recessional condition; and, second, that this 
main recession was itself nearly if not perfectly regular. It is possible, 
h owever, that the general recession had a slowly accelerating rate. 
