350 The American Geologist. •'"°^' ^^^^ 
My consideration of this question, in the first of the 
two papers cited as published in -1900, is stated as follows: 
The very long Tertiary era, preceding the Ice age, had permitted 
the larger streams of Minnesota and Wisconsin to erode deep and 
wide, well matured valleys, free from waterfalls or strong rapids, 
and having no narrow, rock-walled gorges, like the Dalles of the 
St. Croix. But in the northern drift-covered part of the United 
States, and throughout Canada, the rivers, on their again coming 
into existence when the ice of the Glacial period melted away, 
found themselves in many places turned aside from their preglacial 
courses by the drift deposits and by the movements of continental 
uplift and subsidence that were associated with the Ice age. In 
some cases formerly independent streams were thus united to make 
a single larger river system; and often a river was turned out of its 
old drift-filled valley for a comparatively short distance, as a few 
miles, being there compelled to cut a new gorge in the bed-rocks. 
One or the other of these results of the Glacial period has been 
well ascertained as the fortune of so many rivers in the great drift- 
covered region that the occurrence of the two short, grandly pic- 
turesque rock gorges, or canons, known as the Upper and Lower 
Dalles of the St. Croix, so named by the French voyageurs in allu- 
sion to their inclosing walls of rock, strongly suggests that there 
the stream is now flowing in a course which it has cut during and 
since the Ice age. No closely adjacent belt, however, seems to be 
probably identifiable as a drift-filled preglacial valley. Therefore, 
from my studies, for the Minnesota Geological Survey, of the coun- 
try extending many miles westward from the St. Croix, I conclude 
that in preglacial times this river was represented by two quite 
independent rivers, each flowing into the Mississippi. 
The greater part of the St. Croix drainage basin, including all 
above the rapids, six miles long, which end at St. Croix Falls and 
Taylor's Falls, I think to have belonged before the Ice age to a, river 
flowing south and southwest from the principal elbow of the present 
St. Croix, taking approximately the course of the Sunrise river, 
which, however, now runs northward, and traversing Anoka county 
to a junction with the Mississippi somewhere between Anoka and 
Minneapolis. Thence, as Prof. N. H. Winchell has shown, the 
preglacial course of the Mississippi probably passed southeastward.* 
* * * * 
A broad, low belt of sand and gravel plains stretches across 
the distance of nearly 40 miles from the St. Croix to the Missis- 
sippi at Anoka, nowhere having a greater hight than 150 feet above 
» An Approximate Interglacial Chi onometer, Am. Geologist, vol. x 
pp. 69-80, with sections and a map, August, 1892. On this map the 
probable preglacial and Interglacial channels of the Mississippi in the 
vicinity of Minneapolis and St. Paul are delineated, differing much from 
its present course. 
