IOWA CAMBRIC SUCCESSION 
323 
sandstone. To these in correlation all other strata have to be 
sooner or later referred. A few years ago when it was found im¬ 
possible from the literature alone satisfactorily to parallel the 
Iowa and Minnesota Cambric sections there was undertaken a 
special inspection of type localities in the Minnesota River valley. 
The gorge was followed from Mankato to St. Paul. There 
seemed to be no trouble in recognizing in the so-called St. Law¬ 
rence limestone the superior portion of the Oneota Dolomite of 
northeastern Iowa; and in the Jordan Sandstone the layer which 
at one time by error farther south had been called by Winchell 
the New Richmond terrane. 
Although the St. Lawrence Dolomite was found exposed only 
for a distance of a few feet above the water level of the river 
well-records of the neighborhood showed conclusively that the 
formation was really very thick, usually over 150 feet. Suspi¬ 
cions were at once aroused that this was indeed the “main body” 
of dolomite. On the basis of this hypothesis the bed was traced 
eastward and southeastward into Iowa. Winchell’s early rock 
nomenclature in the southeastern counties of Minnesota appeared 
to be correct. Some of the Iowa correlations were certainly 
wrong. Small wonder that Hall and Sardeson have to conclude 
that “The St. Lawrence and Oneota Dolomites have a large pro¬ 
portion of their known organic remains in common.” 
It was these manifest uncertainties in published correlations 
concerning the Cambric terranes which, in the early reports of the 
present Iowa Geological Survey, led to the usage of only the 
larger subdivisional names, and the extension of McGee’s Oneota 
Dolomite to cover the whole of Owen’s Lower Magnesian Lime¬ 
stone. 
When, as a geological title the name Jordan was first intro¬ 
duced by Alexander Winchell,^® in 1872, in connection with an ac¬ 
count of certain brine wells, located 50 miles southwest of St. 
Paul, in the valley of Minnesota River, it designated an arena¬ 
ceous bed about 25 feet thick, which occupied at the town of 
Jordan the bottom of a stream valley, the cliffs above being form¬ 
ed of gray dolomites. For a distance of many miles northeast of 
48 Bull. Geol. Soc. America, Vol. VI, p. 198, 1895. 
49 Kept. Geol. Surv. of Vicinity of Belleplaine, Scott, Co. Minn., Pamphlet, 16 
pp., St. Paul, 1872. 
