WIENS, JARI CIVNCIVAIL, WAILILI VS Ole WIBUS MOCSSIUSSINP 
AUINID) IES WIRIOS IO IAIRIUE;S.. 
Ir 1s the purpose of this paper to bring together such data as 
are available on the subject of preglacial drainage lines, in the 
northern part of the Mississippi basin. It is thought that such a 
presentation will aid in drawing inferences concerning several 
important questions connected with glaciation; among which are 
the preglacial altitude of the region, the differential crust move- 
ments, and the effect of glaciation in enlarging and deepening 
valleys. It will be mainly a contribution of facts. The ques- 
tions upon which these facts have a bearing need the full light 
of these and other data before inferences of much value can be 
drawn. 
This district has, in some respects, advantages not possessed 
by other districts. (1) It has a driftless area in which the 
breadth and depth of large preglacial valleys can be accurately 
determined. The location of this driftless area is particularly 
fortunate, being over the line of so prominent a valley as the 
Mississippi, a valley which crosses drift-covered areas both above 
and below the driftless area. (2) In some parts of the glaciated 
region the oldest drift sheets are not well represented, and it 
often becomes difficult to decide whether a given valley was cut 
to its present depth in preglacial time or has been deepened in 
inter-glacial or post-glacial times. In the region here discussed 
some of the valleys are filled with the oldest drift sheet of which 
we have knowledge, and their floors have not since been subject 
to the scour of streams. We can, therefore, confidently place 
their excavation before the first ice invasion. (3) In this region 
the valleys of some of the main arteries of preglacial drainage 
are found running parallel with the longer axis of one of the 
deepest lake basins, the basin of Lake Michigan. A study of the 
contours of these valleys, combined with a study of the lake 
basin should help to an understanding of the influence of the ice- 
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