Artesian Water for Minneapolis. — Winchell. 273 
Trenton limestone is wanting. It is found also that the St. 
Peter sandstone itself is very much reduced in thickness and 
that there is quite an accumulation of drift materials upon the 
remaining portion of the St. Peter sandstone throughout this 
belt. It seems that for a long period of time before the Glacial 
period the Mississippi river, instead of flowing over the falls 
of St. Anthony, had a course southwestwardly across the city, 
occupying this excavated portion of the St. Peter sandstone. 
This excavation is known to extend northward up the Missis- 
sippi valley as far as the St. Peter sandstone is know to extend. 
The width of this old gorge, if we disregard the drift filling, 
varies from half a mile to a mile and a half, or perhaps two 
miles, having an average width at least of a mile. 
The drift which lies in this old gorge is frequently a lamin- 
ated fine clay, having a thickness of sometimes fifty feet. It 
can be seen at all the brick yards in the north part of the city, 
and it serves to seal, almost hermetically, the St. Peter sand- 
stone upon which it lies, constituting a barrier against the free 
passage of water from the sandstone upward or from the sur- 
face downward. The area throughout which this gorge is 
known to exist amounts to 1334 square miles in the city limits. 
The structural relations of the drift, whether it be till or 
clay, or gravel and sand, to the St. Peter sandstone and to this 
old gorge are generalized in this diagram : 
Fig. .3 — Water Relations at the Glenwood-Inglewood Springs. 
This diagram shows that the drift, in more or less unmodi- 
fied state, lies upon the Trenton limestone outside of this old 
gorge, and constitutes the higher land to the northwest and to 
the northeast, as well as to the east and west. The surface 
water which falls upon these higher drift deposits, sinking into 
the gravel and sand, is shed in the springs at the top of the 
Trenton limestone wherever the Trenton limestone is exten- 
sive enough and impervious enough to shed it in considerable 
quantity. The surface water which falls upon the brick clay 
area, sinking into the sands which cover the brick clay, is shed 
■either into Bassett's creek or into the Mississippi. 
There are also areas where the till of the drift operates in 
the same manner as the Trenton limestone and in the same way 
as the laminated brick clay to confine water and also to 
shed water. Water which, sinking downward, reaches this till 
