A Strati graphical Study 
131 
(1) These diversions were not due to outlet-erosion of ponded 
j water marginal to Wisconsin ice; this ice-sheet did not reach the 
I area. If subsequent to this period, head-water capture was the 
mode of the diversion. Either differential tilting or warping, or 
the great inequality of volume and load favoring valley-deepening 
by the streams flowing away from the glaciated region, induced 
the piracy. In this case the lowered divide segment of the valley 
should be quite free from alluvium; it should bear no terraces of 
glacial outwash; it should be narrow and gorge-like. 
(2) If the diversion dates from the interval between the two 
ice-invasions, and was brought about in any of the three methods 
just mentioned, the chief difference in the appearance of the 
lowered-divide segment of the valley would be one of age, that is, 
this segment would show a greater amount of weathering corre- 
sponding to the longer time period involved. Whether this seg- 
ment would bear alluvium of ordinary stream-aggraded material, 
or of glacial outwash terraces, depends on the relation these val- 
leys bore to the drainage from the Wisconsin ice. As previously 
stated, it does not seem likely that such drainage existed in the 
area. 
(3) If the diversions were incidental to Illinoian glaciation, 
then the process of diversion must have involved a cutting down 
of the outlets of lakes held up in front of the ice. The depth of 
cutting in the lowered-divide segments of these valleys is so great 
that these hypothecated ice-front lakes must have existed for a 
long period. The basins involved in any one of them was so slight 
that the lakes must have come largely from the melting ice. Lakes 
lower their outlets slowly because outlet streams are almost entirely 
free of cutting tools; the great time involved in this outlet-erosion, 
would insure some evidence of wave-work about the lake shores 
as well as deposition-work of inflowing streams. The interval of 
time since the Illinoian glaciation would not remove completely 
all evidence of such shore-phenomena. 
(4) As evidence of a pre-Illinoian date for these diversions we 
would require {a) greater age than described above in the cross- 
section of the lowered-divide segments of the valleys, {b) glacial 
alluvium present in these segments, (c) unmodified drift grading 
into outwash in, or contiguous to, the captured portions of the 
valleys, and (d) other instances of piracy in the neighboring ungla- 
ciated region representing the same movement in drainage adjust- 
