PLATE XLII. 



HENNEPIN COUNTY, 1888. N. H. WINCHELL. 



Except small patches of prairie along the terrace flats and the plains that accom- 

 pany the valleys of the Mississippi and Minnesota, this county was originally tim- 

 bered, resembling Wright and Carver counties adjoining. There is a large central 

 area, including portions of Corcoran, Medina and Greenwood, which is nearly flat. 

 From this tract the country falls away in a rolling descent in all directions. This 

 more elevated plateau may be underlain by the Trenton limestone, in which case its 

 origin is like numerous buttes that consist primarily of the Trenton and St. Peter 

 sandstone in Goodhue and Dakota counties. Nearly all the rest of the county has 

 a broken surface, excepting only the gravelly plains of the.great rivers. Lake Min- 

 netonka and the numerous other lakes that lie to the north and south of it are in 

 the midst of a morainic belt, the depressions of which are sometimes 200 feet below 

 the hills. 



The falls of St. Anthony are caused by the passage of the Mississippi across the 

 boundary line of the Trenton limestone and the St. Peter sandstone, the erosible 

 sandstone crumbling away and allowing the limestone to project at the brink of 

 the falls. 



The present falls have eroded the gorge from Fort Snelling, but prior to the 

 present gorge another gorge was eroded, which lies through the western part of the 

 city of Minneapolis, running from the mouth of Bassett's creek southwestwardly up 

 that valley to Lake of the Isles, lakes Calhoun and Harriet, and to the Minnesota, 

 probably by the valley of Wood lake in Richfield. The location of this old gorge 

 south of lake Harriet is hypothetical; it may have reached the valley of Nine Mile 

 creek. Still earlier the Mississippi river passed from the mouth of Rice creek, in 

 Anoka county, north of Fridley, directly southeastwardly to St. Paul, entering the 

 present Mississippi at Dayton's bluff. It thus followed the valley of Rice creek to 

 lake Johanna, thence to the depressions occupied now by lakes Josephine and 

 McCarron and thence by the valley that drains southwardly to the Mississippi. This 

 earliest valley is probably that occupied by the Mississippi during that long preglacial 

 time of which we have no history in Minnesota, covering the Upper Silurian, the 

 Devonian and Carboniferous and most of the Mesozoic ages. 



The two glacial till sheets found in Dakota, Goodhue and other counties further 

 south, separated by a soil and remains of forests, prove the occurrence of two glacial 

 epochs, or the division of one grand epoch into two sub-epochs. The first one, judging 

 from the nature of the lowest till in Hennepin county, produced a sheet of ice and 



