318 
IOWA CAMBRIC SUCCESSION 
Norton, the sandrock immediately underlying the lowest marls, or 
beginning at a depth of 2100 feet, and extending to 2200 feet, 
appears to comprise the Hinckley terrane. The bottom is here 
1435 feet below sea-level. 
Judged alone from the brief and rather vague description given 
by Ulrich the term Mt. Simon Sandstone is apparently an exact 
synonym of Upham’s earlier name Hinckley Sandstone. But 
the pre-Cambrian topography is so uneven that horizons many 
hundreds of feet apart may coincide with the ancient erosion sur¬ 
face. For this reason the basal Hinckley Sandstone resting direct ¬ 
ly upon the crystalline complex may attain a very great thickness 
before attaining a level characterized by the coarse grits and 
evenly bedded layers to which Ulrich’s title is especially applicable. 
Simon Sandstone is therefore retained for beds which are much 
higher stratigraphically than the typical Hinckley strata. At Eau 
Clare, Wisconsin, the formation attains a vertical measurement of 
more than 225 feet. 
For some reason or other Wooster’s early title Eau Clare 
Beds^^ never came into general usage in Wisconsin, It would 
probably have continued to remain in oblivion had not Ulrich re¬ 
cently revived it. Quoting from Ulrich manuscripts Walcott 
adopts the name; and it thus becomes a useful title for the sandy 
shales lying immediately beneath the great Dresbach Sandstone. 
As originally proposed by Winchell the title Dresbach desig¬ 
nated a single massive sandstone bed, 125 feet in thickness, which 
was extensively quarried at the railway station of that name in 
Winona County, Minnesota. Subsequently the term was made 
to embrace also extensive greensands above and other sands and 
shales below. In extending the term to the Iowa section there 
was included somewhat more than the great sandstone plate of 
Minnesota. It covered not only the sandstone but the overlying 
soft sandrock and shales as high as the first dolomite. Later 
writers as Twenhofel and Thwaites, expand the title still farther, 
so as to take in the entire sequence down to the pre-Cambrian 
23 Smithsonian Misc, Coll., Vol. lyVII, p. 354, 1914. 
24 Geology of Wisconsin, Vol. IV, p. 110, 1882. 
26 Smithsonian Misc. Coll,, Vol. LVII, p. 354, 1914, 
26 Minnesota Geol. Surv., Final Kept., Vol. II, p. xxii, 1888. 
27 Iowa Geol, Surv., Vol. I, p. 23, 1893. 
28 Journal of Geology, Vol. XXVII, p. 614, 1919. 
