424 FRANK BURSLEY TAYLOR 
only is it ascertained that there are fifteen moraines between 
Cincinnati and Mackinac, but the conditions of glacial motion 
and drift deposition were so simple along the entire line that it 
is substantially certain that the series is full and complete. 
Three more moraines in the same series, but possibly not con- 
secutive, were found north of the straits. In making the count 
the central axes of a connected series of wide open valleys was 
followed—up the Miami valley, down the Maumee, up the 
Detroit and St. Clair and thence northward along the west shore 
of Lake Huron. This course was chosen because the ice motion 
was naturally the freest in the open valleys where the resistance 
was least, and the oscillations of the ice-front were recorded 
there more distinctly than anywhere else. This line avoids all 
interlobate and other morainic complexes and follows the valley 
axes where the amplitude of the peripheral oscillations of the 
ice-sheet was naturally greatest. 
On examining the configuration of the individual moraines 
and on comparing the intervals of distance between them (shown 
on the accompanying map) it is apparent that the principal 
irregularities of the moraine series are due to topographic influ- 
ences. As the ice-sheet crept along it moved forward farthest 
and fastest in low wide valleys like the St. Clair-Detroit valley, 
and it lagged behind on the hills and highlands as on Blue 
Mountain south of Georgian Bay, on the highlands south of the 
Straits of Mackinac, and on the ‘‘thumb”’ between Saginaw Bay 
and the south arm of Lake Huron. The relative width of the 
valley and the relative height of the bounding highlands had a 
considerable effect upon the amplitude of the oscillations at any 
given point. For in a narrow valley, between relatively high 
side lands, as was probably the case toa slight extent in the 
Miami and Sciota valleys, the ice movement was cramped and 
the amplitude of oscillation more or less reduced. The ice-lobes 
that spread away southward from the Huron, Saginaw and Erie 
lake basins were wonderfully sensitive to topography. Differ- 
ences of level of the general land surface over which they moved 
- amounting to as little as a hundred or even fifty feet determined 
