STRATIGRAPHICAL GEOLOGY 
245 
mation, already composed of well-rounded components, well- 
sorted materials, and reduced sandgrains, readily supplied inex¬ 
haustible quantities of characteristic sands which are delivered 
to the sea by rivers and perhaps in part by the winds. 
C. L. Dakf,. 
Complexity of Peter Sandstone. When Owen, in 1852, named 
one ^ of the heavy sandstone formations exposed to the Riviere 
Saint Pierre, now only known as the Minnesota River, it was 
believed that it was a compact unit with no differentiable parts. 
This was the subsequent opinion of all who worked in the upper 
Mississippi Valley for many years afterward. But the notable 
unconformity at the base of the section, as observed in later 
years, clearly indicated that there was history involved other than 
any yet noted. 
When the Ozark region came in for special attention little at¬ 
tempt was ever made to closely parallel any of the lower sand¬ 
stones with the northern Peter sandstone. In the early nineties 
of the last century the impression gained credence that the First 
Sandstone of the early reports of Missouri which had sometimes 
been denominated the St. Peter sandstone, was not really the typ¬ 
ical development of the formation in the north, but something 
more. For this reason, mainly, the title Cap-au-Gres Sandstone 
was used for the nearest Missouri occurrences, in order to recog¬ 
nize the distinction. It was then also found that calcareous beds 
were intercalated in the sandstone section and that only the part 
below the limestone horizon could be probably connected with the 
typical Peter formation of Minnesota. 
Just what the exact stratigraphical equivalency was was not 
then very clear. However, it was certain that the original St. 
Peter section was not a simple lithologic unit, but several. Hence, 
in plotting the general geological section of Iowa Peter sandstones 
were raised to serial rank. The absent sedimentation, represented 
by the unconformity at the base, was thought to cover the Canad¬ 
ian interval of the East. 
Under the title of Minnesotan Series the sandstone succession 
thus acquired higher taxonomic rank, although in Iowa it em¬ 
braced apparently a single formation. In the meanwhile special 
terms designated the several terranes in the serial succession 
