324 
IOWA CAMBRIC SUCCESSION 
the town of Mankato this hard Shakopee formation composes the 
upper wall of the river gorge. Rapid weathering of the friable 
sandstone beneath greatly accentuates the normal relief, and per¬ 
mits the resistant dolomite to form mural escarpments along the 
stream. Near Mankato, where the Minnesota River makes a 
sharp bend, another massive dolomite reaches sky in the bottom of 
the gorge. This exposure is denominated by N. H. Winchell 
the St. Lawrence Limestone. As shown by recently drilled wells 
this last mentioned formation attains a thickness of more than 150 
feet. It is really the main dolomitic body of the Magnesian se¬ 
quence of the region. 
This characteristic sandstone exposed at the station of Jordan 
and originally designated by this name, appears to be the same 
stratum later noted by Woorster,®^ in Wisconsin, and there called 
by him the New Richmond Sandstone. Woorster points out the 
fact that the two formations seemingly hold the same stratigraphic 
position. 
It is the mistaken identification of various sandstones with the 
Jordan Sandstone that is at the bottom of all the correlative con¬ 
fusion concerning the Cambric formations of Minnesota. When 
in the deep drill-wells in St. Paul, Upham fancied that he recog¬ 
nized the thinned New Richmond Sandstone of the Wisconsin sec¬ 
tion, he at once concluded that it divided the Shakopee Dolomite. 
He especially distinguished it by calling it the “Elevator B” 
sandstone. On the strength of this surmise Winchell immediately 
proceeded to revise the Cambric succession throughout the state. 
In all of the southeastern counties he regarded the Jordan sand¬ 
stone as erroneously identified.®® It now transpires that only in 
these localities really is the succession correctly interpreted. 
In Houston,®* Winona,®® Filmore,®® and neighboring counties 
situated near Iowa the term Jordan Sandstone is properly applied. 
In Iowa it is the custom to call this terrane the New Richmond 
Sandstone. The typical Jordan Sandstone lies above, instead of 
50 Minnesota Geol. Surv,, Second Ann. Rept., p. 152, 1874. 
51 Wisconsin Geol. Surv., Vol. IV, p. 106, 1882. 
52 Minnesota Geol. Surv., Final Kept., Vol. II, p. xxii, 1888. 
63 Minnesota Geol. Surv., Final Kept., Vol. II, p. xxii, 1888. 
54 Minnesota Geol. Surv., Final Kept., Vol. I, p. 221, 1884. 
55 Ibid., Vol. I, p. 252. 
66 Ibid., Vol. I, p. 287. 
