278 TJie American Geologist. May, i9co 
that Archean granite or schist was reached by the Lakevvood 
well, 1,250 feet below the sea level. 
The Shakopee (also called the Lower Magnesian) lime- 
stone includes, in its middle part, the New Richmond sand- 
stone, of variable thickness, up to 40 feet noted by Hall in the 
. Lakewood record; but in some sections the New Richmond 
horizon is so dolomitic as to be scarcely discriminated. 
The Jordan, St. Lawrence, Dresbach, and St. Croix forma- 
tions together constitute the St. Croix series, as defined and 
named by Winchell in his first annual report of the Minneso- 
ta survey in 1872. 
Intekglacial and Postglacial River Erosion. 
Before the Glacial period, and indeed until its Buchanan 
interglacial stage, marked by a great retreat of the ice-sheet 
succeeding its Kansan maximum advance, the area of Minne- 
apolis appears to have had no deep stream course eroded in its 
somewhat uniform expanse of the Trenton limestone and 
shales. During the long interval between the Kansan and 
lowan stages of snow and ice accumulation and extension, the 
Mississippi river, as shown by Prof. N. H. Winchell,* crossed 
the city area from north to south, cutting through the Trenton 
limestone and deeply into the St. Peter sandstone. The inter- 
glacial Mississippi, according to this view, coincided with the 
present river above Bassett creek, but passed from the mouth 
of this creek southwestward along the chain of lakes compris- 
ing the Lake of the Isles, lakes Calhoun and Harriet, and 
Gr?ss and Wood lakes, to a junction with the Minnesota val- 
ley near the mouth of Nine Mile creek, which is so named 
to note its distance from Fort Snelling, at the mouth of the 
Minnesota river. In this interglacial gorge, now filled with 
drift but still indicated by the hollows of the lake series, the 
deep well of Lakewood cemetery, went 256 feet in drift before 
entering the bed rock, showing that the river erosion there re- 
moved the Trenton beds and about 120 feet of the St. Peter 
formation. 
*"An Approximate Interglacial Chronometer," Am. Geologist, vol. 
X, pp. 69-80, with map and sections, August, i8q2, estimating the inter- 
glacial stage as 9,750 years; which is corrected to about 15,000 years in 
the same volume, p. 302, Nov., 1892. 
