2(54 The American Geolixjist. Octobor, i897 
To the west of it, nnd in the direct line of continuation of 
the old Mississippi valley, there is a topographical depres^sion 
which trends for nian}^ miles to the northwest. It is occu- 
pied in places by lakes, the most important of which is lake 
Phalen. This, in my opinion, w^ill probably be found to be 
the ancient course of the Mississippi river. That it is the 
position of a pre-glacial valley is indicated by a deep well at 
the St. Paul Harvester Works, situated in the present topo- 
graphical depression, which penetrated rock at 235 feet be- 
neath the surface or 628 feet above the sea, which is 55 feet 
beneath the present low-water level of the Mississippi river 
at St. Paul. The lake Phalen depression is separated from 
the head of the Mississippi caaon valley by a moraine which 
is evidently based on a comparatively low surface, for it does 
not rise nearly as high as the drift to tiie east or west. As 
seen from the opposite side of the valley, its escarpment or 
bluif at the head of the old canon valley sliows such topogra- 
phy as is usually produced by the erosion of drift. In short, 
all the evidence favors this lake Phalen depression as the 
position of the pre-glacial continuation of the Mississippi 
canon valley. 
From the southeastern corner of St. Paul -to Le Clare in 
Iowa, the Mississippi river is undoubtedly in a pre-glacial 
valley. But as we proceed southward along its course, we 
become more and more strongly impressed with the idea that 
it is relatively too large a stream for its vallej^. That is, 
that in comparison with the canon valleys of tributary 
streams, the gorge is proportionally too small. In the vicin- 
ity of Dubuque we find some very definite evidence on this 
point and I will give it in some detail. 
Standing on the high bluif in the city of Dubuque, we look 
beyond the great river to a remarkably even upland plain in 
southwestern Wisconsin and northwestern Illinois. It is the 
Tertiary peneplain and we stand upon its surface. Sev- 
eral miles above the city this dissected upland plain appears 
to approach almost to the very verge of the steep- walled can- 
on valley, producing bluffs over 250 feet in hight. Directly 
opposite to us, the bluff is but about 160 feet in hight while 
from its summit the land rises by a gradual slope another 100 
feet to the remnant ridges of the Tertiary peneplain one mile 
